Rambdax

Extended version of Rambda(utility library) - Documentation

Rambda is faster and smaller alternative to the popular functional programming library Ramda. - Documentation

Differences between Rambda and Ramdax

Rambdax passthrough all Rambda methods and introduce some new functions.

The idea of Rambdax is to extend Rambda without worring for Ramda compatibility.

Example use

import { compose, map, filter } from 'rambdax'

const result = compose(
  map(x => x * 2),
  filter(x => x > 2)
)([1, 2, 3, 4])
// => [6, 8]

You can test this example in Rambda's REPL

Install
Differences between Rambda and Ramda
API
Changelog

Rambda's advantages

Tree-shaking

Currently Rambda is more tree-shakable than Ramda

Speed

Rambda is generally more performant than Ramda as the benchmarks can prove that.

dot notation for R.path and R.paths

Standard usage of R.path is R.path(['a', 'b'], {a: {b: 1} }).

In Rambda you have the choice to use dot notation(which is arguably more readable):

R.path('a.b', {a: {b: 1} })

comma notation for R.pick and R.omit

Similar to dot notation, but the separator is comma(,) instead of dot(.).

R.pick('a,b', {a: 1 , b: 2, c: 3} })

// No space allowed between properties

Typescript included

Typescript definitions are included in the library, in comparison to Ramda, where you need to additionally install @types/ramda.

More generic methods

Ramda has an overwhelming list of methods, as one could get lost putting all these methods in one's head. Rambda has smaller method counts and that could be seen as advantage.

Click to see the full list of 116 Ramda methods not implemented in Rambda

__
addIndex
ap
aperture
apply
applyTo
ascend
binary
bind
call
comparator
composeK
composeP
composeWith
construct
constructN
contains
countBy
descend
differenceWith
dissocPath
dropLastWhile
dropRepeats
dropRepeatsWith
dropWhile
empty
eqBy
eqProps
evolve
forEachObjIndexed
gt
gte
hasIn
innerJoin
insert
insertAll
into
invert
invertObj
invoker
juxt
keysIn
lift
liftN
lt
lte
mapAccum
mapAccumRight
mapObjIndexed
memoizeWith
mergeAll
mergeDeepLeft
mergeDeepRight
mergeDeepWith
mergeDeepWithKey
mergeLeft
mergeRight
mergeWith
mergeWithKey
move
nAry
nthArg
o
objOf
of
once
or
otherwise
pair
partialRight
partition
pathEq
pathSatisfies
pickBy
pipeK
pipeP
pipeWith
project
propSatisfies
props
reduceBy
reduceRight
reduceWhile
reduced
remove
scan
sequence
sortWith
splitAt
splitWhen
symmetricDifferenceWith
takeLastWhile
takeWhile
andThen
toPairsIn
transduce
traverse
tryCatch
unapply
unary
uncurryN
unfold
union
unionWith
uniqBy
unless
unnest
until
useWith
valuesIn
where
whereEq
xprod
zipWith
thunkify
default

Install

yarn add rambdax
For UMD usage either use ./dist/rambdax.umd.js or the following CDN link:

https://unpkg.com/rambdax@CURRENT_VERSION/dist/rambdax.umd.js

with deno

import {compose, add} from 'https://raw.githubusercontent.com/selfrefactor/rambdax/master/dist/rambdax.esm.js'

Differences between Rambda and Ramda

Rambda's type detects async functions and unresolved Promises. The returned values are 'Async' and 'Promise'.
Rambda's type handles NaN input, in which case it returns NaN.
Rambda's path and paths accept dot notation - 'x.y' same as ['x','y']
Rambda's pick and omit accept comma notation - 'x,y' same as ['x','y']
Rambda's map, reject and forEach can iterate over objects not only arrays.
Rambda's map and filter pass array index as second argument when mapping over arrays.
Rambda's adjust, all, allPass, any, anyPass, findIndex , findLastIndex and reject are passing index as second argument to the predicate function.
Rambda's filter returns empty array with bad input(null or undefined), while Ramda throws.
Ramda's includes will throw an error if input is neither string nor array, while Rambda version will return false.
Ramda's clamp work for letters, while Rambda's method work only for numbers.

If you need more Ramda methods in Rambda, you may either submit a PR or check the extended version of Rambda - Rambdax. In case of the former, you may want to consult with Rambda contribution guidelines.

Benchmarks

Click to expand all benchmark results

There are methods which are benchmarked only with Ramda and Rambda(i.e. no Lodash).

Note that some of these methods, are called with and without curring. This is done in order to give more detailed performance feedback.

The benchmarks results are produced from latest versions of Rambda, Lodash(4.17.15) and Ramda(0.27.0).

method	Rambda	Ramda	Lodash
add	96.29% slower	96.37% slower	🔳
adjust	62.03% slower	🚀 Fastest	🔳
all	🚀 Fastest	94.17% slower	🔳
allPass	🚀 Fastest	99.04% slower	🔳
any	🚀 Fastest	98.24% slower	🔳
anyPass	🚀 Fastest	99.18% slower	🔳
append	🚀 Fastest	81.35% slower	🔳
applySpec	🚀 Fastest	72.7% slower	🔳
assoc	91.44% slower	58.77% slower	🔳
clone	🚀 Fastest	83.88% slower	🔳
compose	🚀 Fastest	96.09% slower	🔳
converge	37.4% slower	🚀 Fastest	🔳
curry	53.49% slower	🚀 Fastest	🔳
curryN	61.91% slower	🚀 Fastest	🔳
defaultTo	🚀 Fastest	59.37% slower	🔳
drop	🚀 Fastest	97.38% slower	🔳
dropLast	🚀 Fastest	96.82% slower	🔳
equals	77.01% slower	79.54% slower	🔳
filter	71.08% slower	88.05% slower	🔳
find	🚀 Fastest	91.09% slower	🔳
findIndex	🚀 Fastest	97.99% slower	🔳
flatten	96.44% slower	95.22% slower	🔳
ifElse	🚀 Fastest	20.75% slower	🔳
includes	🚀 Fastest	69.26% slower	🔳
indexOf	5% slower	84.76% slower	🔳
init	93.98% slower	96.93% slower	🔳
is	🚀 Fastest	14.62% slower	🔳
isEmpty	62.95% slower	93.54% slower	🔳
last	🚀 Fastest	99.63% slower	🔳
lastIndexOf	🚀 Fastest	41.81% slower	🔳
map	34.86% slower	66.26% slower	🔳
match	🚀 Fastest	44.35% slower	🔳
merge	62.84% slower	🚀 Fastest	🔳
none	🚀 Fastest	88.37% slower	🔳
omit	🚀 Fastest	72.52% slower	🔳
over	🚀 Fastest	40.27% slower	🔳
path	6.27% slower	75.23% slower	🔳
pick	🚀 Fastest	23.34% slower	🔳
prop	🚀 Fastest	89.4% slower	🔳
propEq	🚀 Fastest	85.12% slower	🔳
range	95.65% slower	91.05% slower	🔳
reduce	79.04% slower	72.44% slower	🔳
repeat	82.97% slower	94.94% slower	🔳
replace	3.62% slower	34.6% slower	🔳
set	🚀 Fastest	24.15% slower	🔳
sort	🚀 Fastest	62.87% slower	🔳
sortBy	🚀 Fastest	60.94% slower	🔳
split	🚀 Fastest	85.94% slower	🔳
splitEvery	🚀 Fastest	87.31% slower	🔳
take	91.55% slower	97.55% slower	🔳
takeLast	92.62% slower	98.8% slower	🔳
test	🚀 Fastest	94.14% slower	🔳
type	36.31% slower	🚀 Fastest	🔳
uniq	99.13% slower	96.88% slower	🔳
update	40.2% slower	🚀 Fastest	🔳
view	🚀 Fastest	57.13% slower	🔳

Used by

API

add

add(a: number, b: number): number

It adds a and b.

R.add(2, 3) // =>  5

Try the above R.add example in Rambda REPL

All Typescript definitions

add(a: number, b: number): number;
add(a: number): (b: number) => number;

R.add source

export function add(a, b){
  if (arguments.length === 1) return _b => add(a, _b)

  return Number(a) + Number(b)
}

Tests

import { add } from './add'

test('with number', () => {
  expect(add(2, 3)).toEqual(5)
  expect(add(7)(10)).toEqual(17)
})

test('string is bad input', () => {
  expect(add('foo', 'bar')).toBeNaN()
})

test('ramda specs', () => {
  expect(add('1', '2')).toEqual(3)
  expect(add(1, '2')).toEqual(3)
  expect(add(true, false)).toEqual(1)
  expect(add(null, null)).toEqual(0)
  expect(add(undefined, undefined)).toEqual(NaN)
  expect(add(new Date(1), new Date(2))).toEqual(3)
})

Typescript test

import {add} from 'rambda'

describe('add', () => {
  it('number', () => {
    const result = [add(4)(1), add(4, 1)]
    result[0] // $ExpectType number
    result[1] // $ExpectType number
  })
})

adjust

adjust<T>(index: number, replaceFn: (a: T) => T, list: ReadonlyArray<T>): T[]

It replaces index in array list with the result of replaceFn(list[i]).

R.adjust(
  0,
  a => a + 1,
  [0, 100]
) // => [1, 100]

Try the above R.adjust example in Rambda REPL

All Typescript definitions

adjust<T>(index: number, replaceFn: (a: T) => T, list: ReadonlyArray<T>): T[];
adjust<T>(index: number, replaceFn: (a: T) => T): (list: ReadonlyArray<T>) => T[];

R.adjust source

import { curry } from './curry'

function adjustFn(
  index, replaceFn, list
){
  const actualIndex = index < 0 ? list.length + index : index
  if (index >= list.length || actualIndex < 0) return list

  const clone = list.slice()
  clone[ actualIndex ] = replaceFn(clone[ actualIndex ])

  return clone
}

export const adjust = curry(adjustFn)

Tests

import { add } from './add'
import { adjust } from './adjust'

const expected = [ 0, 11, 2 ]

test('without curring', () => {
  expect(adjust(
    1, add(10), [ 0, 1, 2 ]
  )).toEqual(expected)
})

test('with curring type 1 1 1', () => {
  expect(adjust(1)(add(10))([ 0, 1, 2 ])).toEqual(expected)
})

test('with curring type 1 2', () => {
  expect(adjust(1)(add(10), [ 0, 1, 2 ])).toEqual(expected)
})

test('with curring type 2 1', () => {
  expect(adjust(1, add(10))([ 0, 1, 2 ])).toEqual(expected)
})

test('with negative index', () => {
  expect(adjust(
    -2, add(10), [ 0, 1, 2 ]
  )).toEqual(expected)
})

test('when index is out of bounds', () => {
  const list = [ 0, 1, 2, 3 ]
  expect(adjust(
    4, add(1), list
  )).toEqual(list)
  expect(adjust(
    -5, add(1), list
  )).toEqual(list)
})

1 failed Ramda.adjust specs

💥 Reason for the failure: ramda accepts an array-like object

var R = require('../../../../dist/rambda.js');
var eq = require('./shared/eq');

describe('adjust', function() {
  it('accepts an array-like object', function() {
    function args() {
      return arguments;
    }
    eq(R.adjust(2, R.add(1), args(0, 1, 2, 3)), [0, 1, 3, 3]);
  });
});

all

all<T>(predicate: (x: T) => boolean, list: ReadonlyArray<T>): boolean

It returns true, if all members of array list returns true, when applied as argument to predicate function.

const list = [ 0, 1, 2, 3, 4 ]
const predicate = x => x > -1

const result = R.all(predicate, arr)
// => true

Try the above R.all example in Rambda REPL

All Typescript definitions

all<T>(predicate: (x: T) => boolean, list: ReadonlyArray<T>): boolean;
all<T>(predicate: (x: T) => boolean): (list: ReadonlyArray<T>) => boolean;

R.all source

export function all(predicate, list){
  if (arguments.length === 1) return _list => all(predicate, _list)

  for (let i = 0; i < list.length; i++){
    if (!predicate(list[ i ], i)) return false
  }

  return true
}

Tests

import { all } from './all'

const numArr = [ 0, 1, 2, 3, 4 ]

test('when true', () => {
  const fn = x => x > -1

  expect(all(fn)(numArr)).toBeTrue()
})

test('when false', () => {
  const fn = x => x > 2

  expect(all(fn, numArr)).toBeFalse()
})

test('pass index as second argument', () => {
  const indexes = []
  const fn = (x, i) => {
    indexes.push(i)

    return x > 5
  }
  all(fn, [ 10, 12, 14 ])

  expect(indexes).toEqual([ 0, 1, 2 ])
})

Typescript test

import {all} from 'rambda'

describe('all', () => {
  it('happy', () => {
    const x = all<number>(y => {
      y // $ExpectType number
      return y > 0
    })([1, 2, 3])
    x // $ExpectType boolean

    const q = all(y => y > 0, [1, 2, 3]) // $ExpectType boolean

    q // $ExpectType boolean
  })
})

allFalse

allFalse(...inputs: any[]): boolean

It returns true if all inputs arguments are falsy according to R.isFalsy.

Functions are valid inputs, but these functions cannot have their own arguments.

This method is very similar to R.anyFalse, R.anyTrue and R.allTrue

R.allFalse(0, null, [], {}, '', () => false)
// => true

Try the above R.allFalse example in Rambda REPL

All Typescript definitions

allFalse(...inputs: any[]): boolean;

R.allFalse source

import { isTruthy } from './_internals/isTruthy'
import { type } from './type'

export function allFalse(...inputs){
  let counter = 0
  while (counter < inputs.length){
    const x = inputs[ counter ]

    if (type(x) === 'Function'){
      if (isTruthy(x())){
        return false
      }
    } else if (isTruthy(x)){
      return false
    }

    counter++
  }

  return true
}

Tests

import { runTests } from 'helpers-fn'

import { allFalse } from './allFalse'

const first = { ok : [ () => 2 > 10, () => [], () => {}, null, [] ] }
const second = { fail : [ () => 2 > 10, () => [], () => ({ a : 1 }) ] }
const third = { fail : [ () => 2 > 10, () => [], true ] }

const testData = {
  label : 'foo',
  data  : [ first, second, third ],
  fn    : input => allFalse(...input),
}
runTests(testData)

Typescript test

import {allFalse} from 'rambda'

describe('allFalse', () => {
  it('happy', () => {
    const x = allFalse(null, false, undefined, () => false)
    x // $ExpectType boolean
  })
})

allPass

allPass<T>(predicates: ((x: T) => boolean)[]): (input: T) => boolean

It returns true, if all functions of predicates return true, when input is their argument.

const input = {
  a : 1,
  b : 2,
}
const predicates = [
  x => x.a === 1,
  x => x.b === 2,
]
const result = R.allPass(predicates)(input) // => true

Try the above R.allPass example in Rambda REPL

All Typescript definitions

allPass<T>(predicates: ((x: T) => boolean)[]): (input: T) => boolean;

R.allPass source

export function allPass(predicates){
  return input => {
    let counter = 0
    while (counter < predicates.length){
      if (!predicates[ counter ](input)){
        return false
      }
      counter++
    }

    return true
  }
}

Tests

import { allPass } from './allPass'

test('happy', () => {
  const rules = [ x => typeof x === 'number', x => x > 10, x => x * 7 < 100 ]

  expect(allPass(rules)(11)).toBeTrue()

  expect(allPass(rules)(undefined)).toBeFalse()
})

test('when returns true', () => {
  const conditionArr = [ val => val.a === 1, val => val.b === 2 ]

  expect(allPass(conditionArr)({
    a : 1,
    b : 2,
  })).toBeTrue()
})

test('when returns false', () => {
  const conditionArr = [ val => val.a === 1, val => val.b === 3 ]

  expect(allPass(conditionArr)({
    a : 1,
    b : 2,
  })).toBeFalse()
})

Typescript test

import {allPass} from 'rambda'

describe('allPass', () => {
  it('happy', () => {
    const x = allPass<number>([
      y => {
        y // $ExpectType number
        return typeof y === 'number'
      },
      y => {
        return y > 0
      },
    ])(11)

    x // $ExpectType boolean
  })
})

1 failed Ramda.allPass specs

💥 Reason for the failure: ramda returns a curried function whose arity matches that of the highest-arity predicate

var R = require('../../../../dist/rambda.js');
var eq = require('./shared/eq');

describe('allPass', function() {
  var odd = function(n) { return n % 2 !== 0; };
  var lt20 = function(n) { return n < 20; };
  var gt5 = function(n) { return n > 5; };
  var plusEq = function(w, x, y, z) { return w + x === y + z; };
  it('returns a curried function whose arity matches that of the highest-arity predicate', function() {
    eq(R.allPass([odd, gt5, plusEq]).length, 4);
    eq(R.allPass([odd, gt5, plusEq])(9, 9, 9, 9), true);
    eq(R.allPass([odd, gt5, plusEq])(9)(9)(9)(9), true);
  });
});

allTrue

allTrue(...input: any[]): boolean

It returns true if all inputs arguments are truthy according to R.isTruthy.

R.allTrue(1, true, {a: 1}, [1], 'foo', () => true)
// => true

Try the above R.allTrue example in Rambda REPL

All Typescript definitions

allTrue(...input: any[]): boolean;

R.allTrue source

import { isFalsy } from './_internals/isFalsy'
import { type } from './type'

export function allTrue(...inputs){
  let counter = 0
  while (counter < inputs.length){
    const x = inputs[ counter ]

    if (type(x) === 'Function'){
      if (isFalsy(x())){
        return false
      }
    } else if (isFalsy(x)){
      return false
    }

    counter++
  }

  return true
}

Tests

import { allTrue } from './allTrue'

test('with functions', () => {
  const foo = () => 1
  const bar = () => false
  const baz = () => JSON.parse('{sda')
  const result = allTrue(
    foo, bar, baz
  )
  expect(result).toBe(false)
})

test('usage with non boolean', () => {
  const foo = { a : 1 }
  const baz = [ 1, 2, 3 ]

  const result = allTrue(
    foo, foo, baz
  )
  expect(result).toBe(true)
})

test('usage with boolean', () => {
  const foo = 4
  const baz = [ 1, 2, 3 ]

  const result = allTrue(foo > 2, baz.length === 3)
  expect(result).toBe(true)
})

test('escapes early - case 0', () => {
  const foo = undefined
  const result = allTrue(foo, () => foo.a)
  expect(result).toBe(false)
})

test('escapes early - case 1', () => {
  const foo = null
  const result = allTrue(foo, () => foo.a)
  expect(result).toBe(false)
})

test('escapes early - case 2', () => {
  const foo = { a : 'bar' }
  const result = allTrue(
    foo, foo.a, foo.a.b
  )
  expect(result).toBe(false)
})

test('escapes early - case 3', () => {
  const foo = { a : { b : 'foo' } }
  const result = allTrue(
    foo,
    () => foo.a,
    () => foo.a.b
  )
  expect(result).toBe(true)
})

allType

allType(targetType: RambdaTypes): (...input: any[]) => boolean

It returns a function which will return true if all of its inputs arguments belong to targetType.

const targetType = 'String'

const result = R.allType(
  targetType
)('foo', 'bar', 'baz')
// => true

Try the above R.allType example in Rambda REPL

All Typescript definitions

allType(targetType: RambdaTypes): (...input: any[]) => boolean;

R.allType source

import { type } from './type'

export function allType(targetType){
  return (...inputs) => {
    let counter = 0

    while (counter < inputs.length){
      if (type(inputs[ counter ]) !== targetType){
        return false
      }
      counter++
    }

    return true
  }
}

Tests

import { allType } from './allType'

test('when true', () => {
  const result = allType('Array')(
    [ 1, 2, 3 ], [], [ null ]
  )

  expect(result).toBe(true)
})

test('when false', () => {
  const result = allType('String')(
    1, undefined, null, []
  )

  expect(result).toBe(false)
})

always

always<T>(x: T): () => T

It returns function that always returns x.

const fn = R.always(7)

console.log(fn())// => 7

Try the above R.always example in Rambda REPL

All Typescript definitions

always<T>(x: T): () => T;

R.always source

export function always(x){
  return () => x
}

Tests

import { always } from './always'

test('happy', () => {
  const fn = always(7)

  expect(fn()).toEqual(7)
  expect(fn()).toEqual(7)
})

and

and<T extends { and?: ((...a: readonly any[]) => any)

Returns true if both arguments are true. Otherwise, it returns false.

R.and(true, true); // => true
R.and(false, true); // => false

Try the above R.and example in Rambda REPL

All Typescript definitions

and<T extends { and?: ((...a: readonly any[]) => any); } | number | boolean | string | null>(fn1: T, val2: any): boolean;
and<T extends { and?: ((...a: readonly any[]) => any); } | number | boolean | string | null>(fn1: T): (val2: any) => boolean;

R.and source

export function and(a, b){
  if (arguments.length === 1) return _b => and(a, _b)

  return a && b
}

Tests

import { and } from './and'

test('happy', () => {
  expect(and(true, true)).toBe(true)
  expect(and(true, false)).toBe(false)
  expect(and(false, true)).toBe(false)
  expect(and(false, false)).toBe(false)
})

any

any<T>(predicate: (x: T, i: number) => boolean, list: ReadonlyArray<T>): boolean

It returns true, if at least one member of list returns true, when passed to predicate function.

const list = [1, 2, 3]
const predicate = x => x * x > 8
R.any(fn, list)
// => true

Try the above R.any example in Rambda REPL

All Typescript definitions

any<T>(predicate: (x: T, i: number) => boolean, list: ReadonlyArray<T>): boolean;
any<T>(predicate: (x: T) => boolean, list: ReadonlyArray<T>): boolean;
any<T>(predicate: (x: T, i: number) => boolean): (list: ReadonlyArray<T>) => boolean;
any<T>(predicate: (x: T) => boolean): (list: ReadonlyArray<T>) => boolean;

R.any source

export function any(predicate, list){
  if (arguments.length === 1) return _list => any(predicate, _list)

  let counter = 0
  while (counter < list.length){
    if (predicate(list[ counter ], counter)){
      return true
    }
    counter++
  }

  return false
}

Tests

import { any } from './any'

const arr = [ 1, 2 ]

test('no curry', () => {
  expect(any(val => val < 0, arr)).toBeFalse()
})

test('with curry', () => {
  expect(any(val => val < 2)(arr)).toBeTrue()
})

test('passes index to predicate', () => {
  any((x, i) => {
    expect(typeof x).toBe('string')
    expect(typeof i).toBe('number')
  })([ 'foo', 'bar' ])
})

Typescript test

import {any} from 'rambda'

describe('any', () => {
  it('1', () => {
    const x = any<number>(
      (y, i) => {
        y // $ExpectType number
        i // $ExpectType number
        return y > 2
      },
      [1, 2, 3]
    )
    x // $ExpectType boolean
  })
  it('2', () => {
    const x = any<number>(
      y => {
        y // $ExpectType number
        return y > 2
      },
      [1, 2, 3]
    )
    x // $ExpectType boolean
  })

  it('1 curry', () => {
    const x = any<number>((y, i) => {
      y // $ExpectType number
      i // $ExpectType number
      return y > 2
    })([1, 2, 3])
    x // $ExpectType boolean
  })
  it('2 curry', () => {
    const x = any<number>(y => {
      y // $ExpectType number
      return y > 2
    })([1, 2, 3])
    x // $ExpectType boolean
  })
})

anyFalse

anyFalse(...input: any[]): boolean

It returns true if any of inputs is falsy according to R.isFalsy.

R.anyFalse(1, {a: 1}, [1], () => false)
// => true

Try the above R.anyFalse example in Rambda REPL

All Typescript definitions

anyFalse(...input: any[]): boolean;

R.anyFalse source

import { isFalsy } from './_internals/isFalsy'
import { type } from './type'

export function anyFalse(...inputs){
  let counter = 0
  while (counter < inputs.length){
    const x = inputs[ counter ]

    if (type(x) === 'Function'){
      if (isFalsy(x())){
        return true
      }
    } else if (isFalsy(x)){
      return true
    }

    counter++
  }

  return false
}

Tests

import { anyFalse } from './anyFalse'

test('when true', () => {
  expect(anyFalse(
    true, true, false
  )).toBeTruthy()
})

test('when false', () => {
  expect(anyFalse(true, true)).toBeFalsy()
})

test('supports function', () => {
  expect(anyFalse(
    true,
    () => true,
    () => false
  )).toBeTruthy()
})

anyPass

anyPass<T>(predicates: ReadonlyArray<SafePred<T>>): SafePred<T>

It accepts list of predicates and returns a function. This function with its input will return true, if any of predicates returns true for this input.

const isBig = x => x > 20
const isOdd = x => x % 2 === 1
const input = 11

const fn = R.anyPass(
  [isBig, isOdd]
)

const result = fn(input) 
// => true

Try the above R.anyPass example in Rambda REPL

All Typescript definitions

anyPass<T>(predicates: ReadonlyArray<SafePred<T>>): SafePred<T>;

R.anyPass source

export function anyPass(predicates){
  return input => {
    let counter = 0
    while (counter < predicates.length){
      if (predicates[ counter ](input)){
        return true
      }
      counter++
    }

    return false
  }
}

Tests

import { anyPass } from './anyPass'

test('happy', () => {
  const rules = [ x => typeof x === 'string', x => x > 10 ]
  const predicate = anyPass(rules)
  expect(predicate('foo')).toBeTrue()
  expect(predicate(6)).toBeFalse()
})

test('happy', () => {
  const rules = [ x => typeof x === 'string', x => x > 10 ]

  expect(anyPass(rules)(11)).toBeTrue()

  expect(anyPass(rules)(undefined)).toBeFalse()
})

const obj = {
  a : 1,
  b : 2,
}

test('when returns true', () => {
  const conditionArr = [ val => val.a === 1, val => val.a === 2 ]

  expect(anyPass(conditionArr)(obj)).toBeTrue()
})

test('when returns false + curry', () => {
  const conditionArr = [ val => val.a === 2, val => val.b === 3 ]

  expect(anyPass(conditionArr)(obj)).toBeFalse()
})

test('happy', () => {
  expect(anyPass([])(3)).toEqual(false)
})

Typescript test

import {anyPass} from 'rambda'

describe('anyPass', () => {
  it('happy', () => {
    const x = anyPass<number>([
      y => {
        y // $ExpectType number
        return typeof y === 'number'
      },
      y => {
        return y > 0
      },
    ])(11)

    x // $ExpectType boolean
  })
})

1 failed Ramda.anyPass specs

💥 Reason for the failure: ramda returns a curried function whose arity matches that of the highest-arity predicate

var R = require('../../../../dist/rambda.js');
var eq = require('./shared/eq');

describe('anyPass', function() {
  var odd = function(n) { return n % 2 !== 0; };
  var gt20 = function(n) { return n > 20; };
  var lt5 = function(n) { return n < 5; };
  var plusEq = function(w, x, y, z) { return w + x === y + z; };
  it('returns a curried function whose arity matches that of the highest-arity predicate', function() {
    eq(R.anyPass([odd, lt5, plusEq]).length, 4);
    eq(R.anyPass([odd, lt5, plusEq])(6, 7, 8, 9), false);
    eq(R.anyPass([odd, lt5, plusEq])(6)(7)(8)(9), false);
  });
});

anyTrue

anyTrue(...input: any[]): boolean

It returns true if any of inputs arguments are truthy according to R.isTruthy.

R.anyTrue(0, null, [], {}, '', () => true)
// => true

Try the above R.anyTrue example in Rambda REPL

All Typescript definitions

anyTrue(...input: any[]): boolean;

R.anyTrue source

import { isTruthy } from './_internals/isTruthy'
import { type } from './type'

export function anyTrue(...inputs){
  let counter = 0
  while (counter < inputs.length){
    const x = inputs[ counter ]

    if (type(x) === 'Function'){
      if (isTruthy(x())){
        return true
      }
    } else if (isTruthy(x)){
      return true
    }

    counter++
  }

  return false
}

Tests

import { anyTrue } from './anyTrue'

test('when true', () => {
  expect(anyTrue(
    true, true, false
  )).toBeTruthy()
})

test('when false', () => {
  expect(anyTrue(
    false, false, false
  )).toBeFalsy()
})

test('supports function', () => {
  expect(anyTrue(
    false,
    false,
    false,
    () => false,
    () => true
  )).toBeTruthy()
})

anyType

anyType(targetType: RambdaTypes): (...input: any[]) => boolean

It returns a function which will return true if at least one of its inputs arguments belongs to targetType.

targetType is one of the possible returns of R.type

const targetType = 'String'

const result = R.anyType(
  targetType
)(1, {}, 'foo')
// => true

Try the above R.anyType example in Rambda REPL

All Typescript definitions

anyType(targetType: RambdaTypes): (...input: any[]) => boolean;

R.anyType source

import { type } from './type'

export function anyType(targetType){
  return (...inputs) => {
    let counter = 0

    while (counter < inputs.length){
      if (type(inputs[ counter ]) === targetType){
        return true
      }
      counter++
    }

    return false
  }
}

Tests

import { anyType } from './anyType'

test('when true', () => {
  const result = anyType('Array')(
    1, undefined, null, []
  )

  expect(result).toBe(true)
})

test('when false', () => {
  const result = anyType('String')(
    1, undefined, null, []
  )

  expect(result).toBe(false)
})

append

append<T>(x: T, listOrString: ReadonlyArray<T>): T[]

It adds element x at the end of listOrString.

const x = 'foo'

const result = [
  R.append(x, 'cherry_'),
  R.append(x, ['bar', 'baz'])
]
// => ['cherry_foo', ['bar', 'baz', 'foo']]

Try the above R.append example in Rambda REPL

All Typescript definitions

append<T>(x: T, listOrString: ReadonlyArray<T>): T[];
append<T>(x: T): <T>(listOrString: ReadonlyArray<T>) => T[];

R.append source

export function append(x, listOrString){
  if (arguments.length === 1)
    return _listOrString => append(x, _listOrString)

  if (typeof listOrString === 'string') return `${ listOrString }${ x }`

  const clone = listOrString.slice()
  clone.push(x)

  return clone
}

Tests

import { append } from './append'
import { compose } from './compose'
import { flatten } from './flatten'
import { map } from './map'

test('with strings', () => {
  expect(append('o', 'fo')).toEqual('foo')
})

test('with arrays', () => {
  expect(append('tests', [ 'write', 'more' ])).toEqual([
    'write',
    'more',
    'tests',
  ])
})

test('append to empty array', () => {
  expect(append('tests', [])).toEqual([ 'tests' ])
})

test('happy', () => {
  const result = compose(flatten, map(append(0)))([ [ 1 ], [ 2 ], [ 3 ] ])
  expect(result).toEqual([ 1, 0, 2, 0, 3, 0 ])
})

test('should not modify arguments', () => {
  const a = [ 1, 2, 3 ]
  const b = append(4, a)

  expect(a).toEqual([ 1, 2, 3 ])
  expect(b).toEqual([ 1, 2, 3, 4 ])
})

applySpec

applySpec<Spec extends Record<string, (...args: readonly any[]) => any>>(
  spec: Spec
): (
  ...args: Parameters<ValueOfRecord<Spec>>
) => { [Key in keyof Spec]: ReturnType<Spec[Key]> }

It returns a curried function with the same arity as the longest function in the spec object. Arguments will be applied to the spec methods recursively.

const spec = {
  name: R.path('deeply.nested.firstname')
}
const json = {
  deeply: {
   nested: {
      firstname: 'barry'
    }
  }
}
const result = R.applySpec(spec, json) // => { name: 'barry' }

// Second example
const getMetrics = R.applySpec({
  sum: R.add,
  nested: { mul: R.multiply }
})
getMetrics(2, 4) 
// => { sum: 6, nested: { mul: 8 } }

Try the above R.applySpec example in Rambda REPL

All Typescript definitions

applySpec<Spec extends Record<string, (...args: readonly any[]) => any>>(
  spec: Spec
): (
  ...args: Parameters<ValueOfRecord<Spec>>
) => { [Key in keyof Spec]: ReturnType<Spec[Key]> };
applySpec<T>(spec: any): (...args: readonly any[]) => T;

R.applySpec source

import { _isArray } from './_internals/_isArray'

// recursively traverse the given spec object to find the highest arity function
function __findHighestArity(spec, max = 0){
  for (const key in spec){
    if (spec.hasOwnProperty(key) === false || key === 'constructor') continue

    if (typeof spec[ key ] === 'object'){
      max = Math.max(max, __findHighestArity(spec[ key ]))
    }

    if (typeof spec[ key ] === 'function'){
      max = Math.max(max, spec[ key ].length)
    }
  }

  return max
}

function __filterUndefined(){
  const defined = []
  let i = 0
  const l = arguments.length
  while (i < l){
    if (typeof arguments[ i ] === 'undefined') break
    defined[ i ] = arguments[ i ]
    i++
  }

  return defined
}

function __applySpecWithArity(
  spec, arity, cache
){
  const remaining = arity - cache.length

  if (remaining === 1)
    return x =>
      __applySpecWithArity(
        spec, arity, __filterUndefined(...cache, x)
      )
  if (remaining === 2)
    return (x, y) =>
      __applySpecWithArity(
        spec, arity, __filterUndefined(
          ...cache, x, y
        )
      )
  if (remaining === 3)
    return (
      x, y, z
    ) =>
      __applySpecWithArity(
        spec, arity, __filterUndefined(
          ...cache, x, y, z
        )
      )
  if (remaining === 4)
    return (
      x, y, z, a
    ) =>
      __applySpecWithArity(
        spec,
        arity,
        __filterUndefined(
          ...cache, x, y, z, a
        )
      )
  if (remaining > 4)
    return (...args) =>
      __applySpecWithArity(
        spec, arity, __filterUndefined(...cache, ...args)
      )

  // handle spec as Array
  if (_isArray(spec)){
    const ret = []
    let i = 0
    const l = spec.length
    for (; i < l; i++){
      // handle recursive spec inside array
      if (typeof spec[ i ] === 'object' || _isArray(spec[ i ])){
        ret[ i ] = __applySpecWithArity(
          spec[ i ], arity, cache
        )
      }
      // apply spec to the key
      if (typeof spec[ i ] === 'function'){
        ret[ i ] = spec[ i ](...cache)
      }
    }

    return ret
  }

  // handle spec as Object
  const ret = {}
  // apply callbacks to each property in the spec object
  for (const key in spec){
    if (spec.hasOwnProperty(key) === false || key === 'constructor') continue

    // apply the spec recursively
    if (typeof spec[ key ] === 'object'){
      ret[ key ] = __applySpecWithArity(
        spec[ key ], arity, cache
      )
      continue
    }

    // apply spec to the key
    if (typeof spec[ key ] === 'function'){
      ret[ key ] = spec[ key ](...cache)
    }
  }

  return ret
}

export function applySpec(spec, ...args){
  // get the highest arity spec function, cache the result and pass to __applySpecWithArity
  const arity = __findHighestArity(spec)

  if (arity === 0){
    return () => ({})
  }
  const toReturn = __applySpecWithArity(
    spec, arity, args
  )

  return toReturn
}

Tests

import { applySpec as applySpecRamda, nAry } from 'ramda'

import { add, always, compose, dec, inc, map, path, prop, T } from '../rambda'
import { applySpec } from './applySpec'

test('different than Ramda when bad spec', () => {
  const result = applySpec({ sum : { a : 1 } })(1, 2)
  const ramdaResult = applySpecRamda({ sum : { a : 1 } })(1, 2)
  expect(result).toEqual({})
  expect(ramdaResult).toEqual({ sum : { a : {} } })
})

test('works with empty spec', () => {
  expect(applySpec({})()).toEqual({})
  expect(applySpec([])(1, 2)).toEqual({})
  expect(applySpec(null)(1, 2)).toEqual({})
})

test('works with unary functions', () => {
  const result = applySpec({
    v : inc,
    u : dec,
  })(1)
  const expected = {
    v : 2,
    u : 0,
  }
  expect(result).toEqual(expected)
})

test('works with binary functions', () => {
  const result = applySpec({ sum : add })(1, 2)
  expect(result).toEqual({ sum : 3 })
})

test('works with nested specs', () => {
  const result = applySpec({
    unnested : always(0),
    nested   : { sum : add },
  })(1, 2)
  const expected = {
    unnested : 0,
    nested   : { sum : 3 },
  }
  expect(result).toEqual(expected)
})

test('works with arrays of nested specs', () => {
  const result = applySpec({
    unnested : always(0),
    nested   : [ { sum : add } ],
  })(1, 2)

  expect(result).toEqual({
    unnested : 0,
    nested   : [ { sum : 3 } ],
  })
})

test('works with arrays of spec objects', () => {
  const result = applySpec([ { sum : add } ])(1, 2)

  expect(result).toEqual([ { sum : 3 } ])
})

test('works with arrays of functions', () => {
  const result = applySpec([ map(prop('a')), map(prop('b')) ])([
    {
      a : 'a1',
      b : 'b1',
    },
    {
      a : 'a2',
      b : 'b2',
    },
  ])
  const expected = [
    [ 'a1', 'a2' ],
    [ 'b1', 'b2' ],
  ]
  expect(result).toEqual(expected)
})

test('works with a spec defining a map key', () => {
  expect(applySpec({ map : prop('a') })({ a : 1 })).toEqual({ map : 1 })
})

test.skip('retains the highest arity', () => {
  const f = applySpec({
    f1 : nAry(2, T),
    f2 : nAry(5, T),
  })
  expect(f.length).toBe(5)
})

test('returns a curried function', () => {
  expect(applySpec({ sum : add })(1)(2)).toEqual({ sum : 3 })
})

// Additional tests
// ============================================
test('arity', () => {
  const spec = {
    one   : x1 => x1,
    two   : (x1, x2) => x1 + x2,
    three : (
      x1, x2, x3
    ) => x1 + x2 + x3,
  }
  expect(applySpec(
    spec, 1, 2, 3
  )).toEqual({
    one   : 1,
    two   : 3,
    three : 6,
  })
})

test('arity over 5 arguments', () => {
  const spec = {
    one   : x1 => x1,
    two   : (x1, x2) => x1 + x2,
    three : (
      x1, x2, x3
    ) => x1 + x2 + x3,
    four : (
      x1, x2, x3, x4
    ) => x1 + x2 + x3 + x4,
    five : (
      x1, x2, x3, x4, x5
    ) => x1 + x2 + x3 + x4 + x5,
  }
  expect(applySpec(
    spec, 1, 2, 3, 4, 5
  )).toEqual({
    one   : 1,
    two   : 3,
    three : 6,
    four  : 10,
    five  : 15,
  })
})

test('curried', () => {
  const spec = {
    one   : x1 => x1,
    two   : (x1, x2) => x1 + x2,
    three : (
      x1, x2, x3
    ) => x1 + x2 + x3,
  }
  expect(applySpec(spec)(1)(2)(3)).toEqual({
    one   : 1,
    two   : 3,
    three : 6,
  })
})

test('curried over 5 arguments', () => {
  const spec = {
    one   : x1 => x1,
    two   : (x1, x2) => x1 + x2,
    three : (
      x1, x2, x3
    ) => x1 + x2 + x3,
    four : (
      x1, x2, x3, x4
    ) => x1 + x2 + x3 + x4,
    five : (
      x1, x2, x3, x4, x5
    ) => x1 + x2 + x3 + x4 + x5,
  }
  expect(applySpec(spec)(1)(2)(3)(4)(5)).toEqual({
    one   : 1,
    two   : 3,
    three : 6,
    four  : 10,
    five  : 15,
  })
})

test('undefined property', () => {
  const spec = { prop : path([ 'property', 'doesnt', 'exist' ]) }
  expect(applySpec(spec, {})).toEqual({ prop : undefined })
})

test('restructure json object', () => {
  const spec = {
    id          : path('user.id'),
    name        : path('user.firstname'),
    profile     : path('user.profile'),
    doesntExist : path('user.profile.doesntExist'),
    info        : { views : compose(inc, prop('views')) },
    type        : always('playa'),
  }

  const data = {
    user : {
      id        : 1337,
      firstname : 'john',
      lastname  : 'shaft',
      profile   : 'shaft69',
    },
    views : 42,
  }

  expect(applySpec(spec, data)).toEqual({
    id          : 1337,
    name        : 'john',
    profile     : 'shaft69',
    doesntExist : undefined,
    info        : { views : 43 },
    type        : 'playa',
  })
})

Typescript test

import {multiply, applySpec, inc, dec, add} from 'rambda'

describe('applySpec', () => {
  it('ramda 1', () => {
    const result = applySpec({
      v: inc,
      u: dec,
    })(1)
    result // $ExpectType { v: number; u: number; }
  })
  it('ramda 1', () => {
    interface Output {
      sum: number,
      multiplied: number,
    }
    const result = applySpec<Output>({
      sum: add,
      multiplied: multiply,
    })(1, 2)

    result // $ExpectType Output
  })
})

assoc

assoc<T, U, K extends string>(prop: K, newValue: T, obj: U): Record<K, T> & U

It makes a shallow clone of obj with setting or overriding the property prop with newValue.

R.assoc('c', 3, {a: 1, b: 2})
//=> {a: 1, b: 2, c: 3}

Try the above R.assoc example in Rambda REPL

All Typescript definitions

assoc<T, U, K extends string>(prop: K, newValue: T, obj: U): Record<K, T> & U;
assoc<T, K extends string>(prop: K, newValue: T): <U>(obj: U) => Record<K, T> & U;
assoc<K extends string>(prop: K): <T, U>(newValue: T, obj: U) => Record<K, T> & U;

R.assoc source

import { curry } from './curry'

function assocFn(
  prop, newValue, obj
){
  return Object.assign(
    {}, obj, { [ prop ] : newValue }
  )
}

export const assoc = curry(assocFn)

Tests

import { assoc } from './assoc'

test('adds a key to an empty object', () => {
  expect(assoc(
    'a', 1, {}
  )).toEqual({ a : 1 })
})

test('adds a key to a non-empty object', () => {
  expect(assoc(
    'b', 2, { a : 1 }
  )).toEqual({
    a : 1,
    b : 2,
  })
})

test('adds a key to a non-empty object - curry case 1', () => {
  expect(assoc('b', 2)({ a : 1 })).toEqual({
    a : 1,
    b : 2,
  })
})

test('adds a key to a non-empty object - curry case 2', () => {
  expect(assoc('b')(2, { a : 1 })).toEqual({
    a : 1,
    b : 2,
  })
})

test('adds a key to a non-empty object - curry case 3', () => {
  const result = assoc('b')(2)({ a : 1 })

  expect(result).toEqual({
    a : 1,
    b : 2,
  })
})

test('changes an existing key', () => {
  expect(assoc(
    'a', 2, { a : 1 }
  )).toEqual({ a : 2 })
})

test('undefined is considered an empty object', () => {
  expect(assoc(
    'a', 1, undefined
  )).toEqual({ a : 1 })
})

test('null is considered an empty object', () => {
  expect(assoc(
    'a', 1, null
  )).toEqual({ a : 1 })
})

test('value can be null', () => {
  expect(assoc(
    'a', null, null
  )).toEqual({ a : null })
})

test('value can be undefined', () => {
  expect(assoc(
    'a', undefined, null
  )).toEqual({ a : undefined })
})

test('assignment is shallow', () => {
  expect(assoc(
    'a', { b : 2 }, { a : { c : 3 } }
  )).toEqual({ a : { b : 2 } })
})

assocPath

assocPath<T, U>(path: Path, newValue: T, obj: U): U

It makes a shallow clone of obj with setting or overriding with newValue the property found with path.

const path = 'b.c'
const newValue = 2
const obj = { a: 1 }

R.assocPath(path, newValue, obj)
// => { a : 1, b : { c : 2 }}

Try the above R.assocPath example in Rambda REPL

All Typescript definitions

assocPath<T, U>(path: Path, newValue: T, obj: U): U;
assocPath<T, U>(path: Path, newValue: T): (obj: U) => U;
assocPath<T, U>(path: Path): FunctionToolbelt.Curry<(a: T, b: U) => U>;

R.assocPath source

import { _isArray } from './_internals/_isArray'
import { _isInteger } from './_internals/_isInteger'
import { assoc } from './assoc'
import { curry } from './curry'

function assocPathFn(
  list, newValue, input
){
  const pathArrValue = typeof list === 'string' ? list.split('.') : list
  if (pathArrValue.length === 0){
    return newValue
  }

  const index = pathArrValue[ 0 ]
  if (pathArrValue.length > 1){
    const condition =
      typeof input !== 'object' ||
      input === null ||
      !input.hasOwnProperty(index)

    const nextinput = condition ?
      _isInteger(parseInt(pathArrValue[ 1 ], 10)) ?
        [] :
        {} :
      input[ index ]
    newValue = assocPathFn(
      Array.prototype.slice.call(pathArrValue, 1),
      newValue,
      nextinput
    )
  }

  if (_isInteger(parseInt(index, 10)) && _isArray(input)){
    const arr = input.slice()
    arr[ index ] = newValue

    return arr
  }

  return assoc(
    index, newValue, input
  )
}

export const assocPath = curry(assocPathFn)

Tests

import { assocPath } from './assocPath'

test('adds a key to an empty object', () => {
  expect(assocPath(
    'a', 1, {}
  )).toEqual({ a : 1 })
})

test('adds a key to a non-empty object', () => {
  expect(assocPath(
    'b', 2, { a : 1 }
  )).toEqual({
    a : 1,
    b : 2,
  })
})

test('adds a nested key to a non-empty object', () => {
  expect(assocPath(
    'b.c', 2, { a : 1 }
  )).toEqual({
    a : 1,
    b : { c : 2 },
  })
})

test('adds a nested key to a nested non-empty object - curry case 1', () => {
  expect(assocPath('b.d',
    3)({
    a : 1,
    b : { c : 2 },
  })).toEqual({
    a : 1,
    b : {
      c : 2,
      d : 3,
    },
  })
})

test('adds a key to a non-empty object - curry case 1', () => {
  expect(assocPath('b', 2)({ a : 1 })).toEqual({
    a : 1,
    b : 2,
  })
})

test('adds a nested key to a non-empty object - curry case 1', () => {
  expect(assocPath('b.c', 2)({ a : 1 })).toEqual({
    a : 1,
    b : { c : 2 },
  })
})

test('adds a nested array to a non-empty object - curry case 1', () => {
  expect(assocPath('b.0', 2)({ a : 1 })).toEqual({
    a : 1,
    b : [ 2 ],
  })
})

test('adds a key to a non-empty object - curry case 2', () => {
  expect(assocPath('b')(2, { a : 1 })).toEqual({
    a : 1,
    b : 2,
  })
})

test('adds a key to a non-empty object - curry case 3', () => {
  const result = assocPath('b')(2)({ a : 1 })

  expect(result).toEqual({
    a : 1,
    b : 2,
  })
})

test('changes an existing key', () => {
  expect(assocPath(
    'a', 2, { a : 1 }
  )).toEqual({ a : 2 })
})

test('undefined is considered an empty object', () => {
  expect(assocPath(
    'a', 1, undefined
  )).toEqual({ a : 1 })
})

test('null is considered an empty object', () => {
  expect(assocPath(
    'a', 1, null
  )).toEqual({ a : 1 })
})

test('value can be null', () => {
  expect(assocPath(
    'a', null, null
  )).toEqual({ a : null })
})

test('value can be undefined', () => {
  expect(assocPath(
    'a', undefined, null
  )).toEqual({ a : undefined })
})

test('assignment is shallow', () => {
  expect(assocPath(
    'a', { b : 2 }, { a : { c : 3 } }
  )).toEqual({ a : { b : 2 } })
})

test('happy', () => {
  const result = assocPath(
    [], 3, {
      a : 1,
      b : 2,
    }
  )
  expect(result).toEqual(3)
})

test('happy', () => {
  const expected = { foo : { bar : { baz : 42 } } }
  const result = assocPath(
    [ 'foo', 'bar', 'baz' ], 42, { foo : null }
  )
  expect(result).toEqual(expected)
})

both

both(pred1: Pred, pred2: Pred): Pred

It returns a function with input argument.

This function will return true, if both firstCondition and secondCondition return true when input is passed as their argument.

const firstCondition = x => x > 10
const secondCondition = x => x < 20
const fn = R.both(secondCondition)

const result = [fn(15), fn(30)]
// => [true, false]

Try the above R.both example in Rambda REPL

All Typescript definitions

both(pred1: Pred, pred2: Pred): Pred;
both<T>(pred1: Predicate<T>, pred2: Predicate<T>): Predicate<T>;
both<T>(pred1: Predicate<T>): (pred2: Predicate<T>) => Predicate<T>;
both(pred1: Pred): (pred2: Pred) => Pred;

R.both source

export function both(f, g){
  if (arguments.length === 1) return _g => both(f, _g)

  return (...input) => f(...input) && g(...input)
}

Tests

import { both } from './both'

const firstFn = val => val > 0
const secondFn = val => val < 10

test('with curry', () => {
  expect(both(firstFn)(secondFn)(17)).toBeFalse()
})

test('without curry', () => {
  expect(both(firstFn, secondFn)(7)).toBeTrue()
})

test('with multiple inputs', () => {
  const between = function (
    a, b, c
  ){
    return a < b && b < c
  }
  const total20 = function (
    a, b, c
  ){
    return a + b + c === 20
  }
  const fn = both(between, total20)
  expect(fn(
    5, 7, 8
  )).toBeTrue()
})

test('skip evaluation of the second expression', () => {
  let effect = 'not evaluated'
  const F = function (){
    return false
  }
  const Z = function (){
    effect = 'Z got evaluated'
  }
  both(F, Z)()

  expect(effect).toBe('not evaluated')
})

Typescript test

import {both} from 'rambda'

describe('both', () => {
  it('with passed type', () => {
    const fn = both<number>( // $ExpectType Predicate<number>
      x => {
        return x > 1
      },
      x => {
        return x % 2 === 0
      }
    )
    const result = fn(2) // $ExpectType boolean
    result // $ExpectType boolean
  })
  it('no type passed', () => {
    const fn = both(
      x => {
        x // $ExpectType any
        return x > 1
      },
      x => {
        return x % 2 === 0
      }
    )
    const result = fn(2) // $ExpectType boolean
    result // $ExpectType boolean
  })
})

describe('both + curry', () => {
  it('with passed type', () => {
    const fn = both<number>(x => {
      return x > 1
    })(x => {
      return x % 2 === 0
    })
    fn // $ExpectType Predicate<number>
    const result = fn(2) // $ExpectType boolean
    result // $ExpectType boolean
  })
  it('no type passed', () => {
    const fn = both(x => {
      x // $ExpectType unknown
      return (x as number) > 1
    })(x => {
      return (x as number) % 2 === 0
    })
    const result = fn(2) // $ExpectType boolean
    result // $ExpectType boolean
  })
})

1 failed Ramda.both specs

💥 Reason for the failure: ramda supports fantasy-land

var S = require('sanctuary');

var R = require('../../../../dist/rambda.js');
var eq = require('./shared/eq');
describe('both', function() {
  it('accepts fantasy-land applicative functors', function() {
    var Just = S.Just;
    var Nothing = S.Nothing;
    eq(R.both(Just(true), Just(true)), Just(true));
    eq(R.both(Just(true), Just(false)), Just(false));
    eq(R.both(Just(true), Nothing()), Nothing());
    eq(R.both(Nothing(), Just(false)), Nothing());
    eq(R.both(Nothing(), Nothing()), Nothing());
  });
});

chain

chain<T, U>(fn: (n: T) => readonly U[], list: readonly T[]): U[]

The method is also known as flatMap.

const duplicate = n => [ n, n ]
const list = [ 1, 2, 3 ]

const result = chain(duplicate, list)
// => [ 1, 1, 2, 2, 3, 3 ]

Try the above R.chain example in Rambda REPL

All Typescript definitions

chain<T, U>(fn: (n: T) => readonly U[], list: readonly T[]): U[];
chain<T, U>(fn: (n: T) => readonly U[]): (list: readonly T[]) => U[];
chain<X0, X1, R>(fn: (x0: X0, x1: X1) => R, fn1: (x1: X1) => X0): (x1: X1) => R;

R.chain source

export function chain(fn, list){
  if (arguments.length === 1){
    return _list => chain(fn, _list)
  }

  return [].concat(...list.map(fn))
}

Tests

import { chain } from './chain'

const duplicate = n => [ n, n ]

test('happy', () => {
  const fn = x => [ x * 2 ]
  const list = [ 1, 2, 3 ]

  const result = chain(fn, list)

  expect(result).toEqual([ 2, 4, 6 ])
})

test('maps then flattens one level', () => {
  expect(chain(duplicate, [ 1, 2, 3 ])).toEqual([ 1, 1, 2, 2, 3, 3 ])
})

test('maps then flattens one level - curry', () => {
  expect(chain(duplicate)([ 1, 2, 3 ])).toEqual([ 1, 1, 2, 2, 3, 3 ])
})

test('flattens only one level', () => {
  const nest = n => [ [ n ] ]
  expect(chain(nest, [ 1, 2, 3 ])).toEqual([ [ 1 ], [ 2 ], [ 3 ] ])
})

Typescript test

import {chain} from 'rambda'

const list = [1, 2, 3]
const duplicate = (n: number) => [n, n]

describe('chain', () => {
  it('without passing type', () => {
    const result = chain(duplicate, list)
    result // $ExpectType number[]
  })

  it('passing types', () => {
    const duplicateAndModify = (x: number) => [`||${x}||`, `||${x}||`]
    const result = chain<number, string>(duplicateAndModify, list)
    const resultCurried = chain<number, string>(duplicateAndModify)(list)
    result // $ExpectType string[]
    resultCurried // $ExpectType string[]
  })
})

5 failed Ramda.chain specs

💥 Reason for the failure: ramda passes to chain if available | ramda supports fantasy-land

change

change<T>(
  origin: object,
  path: string,
  changeData: any
): T

It helps changing object's properties if there are below 3 levels deep.

It is intended for usage inside unit tests, when you need more powerful method to change object's properties.

path input argument allows you to specify which object's sub-branch you want to manipulate. You should pass an empty string if you target the whole origin object.

changeData can be a direct value. If it is a object, then this object is used to edit or add new properties to the selected sub-branch.

const simpleResult = R.change(
  { a: 1, b: { c: 2 } },
  'b.c',
  3
)
const expectedSimpleResult = {
  a: 1,
  b: { c: 3 }
}
// simpleResult === expectedSimpleResult

const origin = {
  a   : 0,
  foo : {
    bar : 1,
    bax : { nested : 2 },
  }
}

const changeData = {
  bar: 2,
  bay: 3,
  bax: { baq: 9 }
}

const result = R.change(
  origin,
  'foo',
  changeData
)

const expected = {
  a   : 0,
  foo : {
    bar : 2,
    bay : 3,
    bax : {
      nested : 2,
      baq: 9
    },
  },
}
// => `result` is equal to `expected`

Try the above R.change example in Rambda REPL

All Typescript definitions

change<T>(
  origin: object,
  path: string,
  changeData: any
): T;
change<Input, Output>(
  origin: Input,
  path: string,
  changeData: any
): Output;

R.change source

//Its lodash's set method taken from
//https://github.com/lodash/lodash/blob/4.5.0-npm-packages
import { _isArray } from './_internals/_isArray'
import { set } from './_internals/set'
import { partition } from './partition'

const isObject = x => {
  const ok = x !== null && !_isArray(x) && typeof x === 'object'
  if (!ok){
    return false
  }

  return Object.keys(x).length > 0
}

export function change(
  origin, pathRaw, rules
){
  const willReturn = JSON.parse(JSON.stringify(origin))

  if (!isObject(rules)){
    set(
      willReturn, pathRaw, rules
    )

    return willReturn
  }
  const path = pathRaw === '' ? '' : `${ pathRaw }.`

  for (const ruleKey of Object.keys(rules)){
    const rule = rules[ ruleKey ]
    if (!isObject(rule)){
      set(
        willReturn, `${ path }${ ruleKey }`, rule
      )
      continue
    }
    const [ withObjects, withoutObjects ] = partition(subruleKey => isObject(rule[ subruleKey ]),
      Object.keys(rule))

    withoutObjects.forEach(subruleKey => {
      const subrule = rule[ subruleKey ]
      set(
        willReturn, `${ path }${ ruleKey }.${ subruleKey }`, subrule
      )
    })

    withObjects.forEach(subruleKey => {
      const subrule = rule[ subruleKey ]
      Object.keys(subrule).forEach(deepKey => {
        const deep = rule[ subruleKey ][ deepKey ]

        if (!isObject(deep)){
          return set(
            willReturn,
            `${ path }${ ruleKey }.${ subruleKey }.${ deepKey }`,
            deep
          )
        }

        Object.keys(deep).forEach(superDeepKey => {
          const superDeep = rule[ subruleKey ][ deepKey ][ superDeepKey ]

          set(
            willReturn,
            `${ path }${ ruleKey }.${ subruleKey }.${ deepKey }.${ superDeepKey }`,
            superDeep
          )
        })
      })
    })
  }

  return willReturn
}

Tests

import { change } from './change'

const origin = {
  a   : 0,
  foo : {
    bar : 1,
    baz : false,
    bax : { nested : 2 },
  },
  first : {
    second : {
      third : {
        fourthA : 3,
        fourthB : 4,
        fourth  : {
          a     : 1,
          fifth : { unreachable : 22 },
        },
      },
    },
  },
}

test('when rule is not an object', () => {
  const expected = {
    a   : 0,
    foo : {
      bar : 1,
      baz : false,
      bax : { nested : 7 },
    },
    first : {
      second : {
        third : {
          fourthA : 3,
          fourthB : 4,
          fourth  : {
            a     : 1,
            fifth : { unreachable : 22 },
          },
        },
      },
    },
  }

  const result = change(
    origin, 'foo.bax.nested', 7
  )
  expect(result).toEqual(expected)
})

test('works with 4 levels deep nesting', () => {
  const changeData = {
    foo : {
      bar : 7,
      bax : { bay : 8 },
    },
    first : {
      second : {
        b     : 7,
        third : {
          fourthA : 9,
          fourth  : { a : 2 },
        },
      },
    },
  }
  const expected = {
    a   : 0,
    foo : {
      bar : 7,
      baz : false,
      bax : {
        nested : 2,
        bay    : 8,
      },
    },
    first : {
      second : {
        third : {
          fourthA : 9,
          fourthB : 4,
          // This is 5th level nesting
          // So we get the full change property
          // Instead of merge with the origin
          ///////////////////////////
          fourth  : { a : 2 },
        },
        b : 7,
      },
    },
  }
  const result = change(
    origin, '', changeData
  )
  expect(result).toEqual(expected)
})

test('simpler', () => {
  const localOrigin = {
    a   : 0,
    foo : {
      bar : 1,
      bax : { nested : 2 },
    },
  }
  const changeData = {
    bar : 2,
    bay : 3,
    bax : { baq : 9 },
  }
  const result = change(
    localOrigin, 'foo', changeData
  )

  const expectedResult = {
    a   : 0,
    foo : {
      bar : 2,
      bay : 3,
      bax : {
        nested : 2,
        baq    : 9,
      },
    },
  }

  expect(result).toEqual(expectedResult)
})

clamp

clamp(min: number, max: number, input: number): number

Restrict a number input to be withing min and max limits.

If input is bigger than max, then the result is max.

If input is smaller than min, then the result is min.

R.clamp(0, 10, 5) //=> 5
R.clamp(0, 10, -1) //=> 0
R.clamp(0, 10, 11) //=> 10

Try the above R.clamp example in Rambda REPL

All Typescript definitions

clamp(min: number, max: number, input: number): number;
clamp(min: number, max: number): (input: number) => number;

R.clamp source

import { curry } from './curry'

function clampFn(
  min, max, input
){
  if (input >= min && input <= max) return input

  if (input > max) return max
  if (input < min) return min
}

export const clamp = curry(clampFn)

Tests

import { clamp } from './clamp'

test('rambda specs', () => {
  expect(clamp(
    1, 10, 0
  )).toEqual(1)
  expect(clamp(
    3, 12, 1
  )).toEqual(3)
  expect(clamp(
    -15, 3, -100
  )).toEqual(-15)
  expect(clamp(
    1, 10, 20
  )).toEqual(10)
  expect(clamp(
    3, 12, 23
  )).toEqual(12)
  expect(clamp(
    -15, 3, 16
  )).toEqual(3)
  expect(clamp(
    1, 10, 4
  )).toEqual(4)
  expect(clamp(
    3, 12, 6
  )).toEqual(6)
  expect(clamp(
    -15, 3, 0
  )).toEqual(0)
})

clone

clone<T>(input: T): T

It creates a deep copy of the input, which may contain (nested) Arrays and Objects, Numbers, Strings, Booleans and Dates.

const objects = [{a: 1}, {b: 2}];
const objectsClone = R.clone(objects);

const result = [
  R.equals(objects, objectsClone),
  R.equals(objects[0], objectsClone[0]),
] // => [ true, true ]

Try the above R.clone example in Rambda REPL

All Typescript definitions

clone<T>(input: T): T;
clone<T>(input: ReadonlyArray<T>): T[];

R.clone source

import { _isArray } from './_internals/_isArray'

export function clone(input){
  const out = _isArray(input) ? Array(input.length) : {}
  if (input && input.getTime) return new Date(input.getTime())

  for (const key in input){
    const v = input[ key ]
    out[ key ] =
      typeof v === 'object' && v !== null ?
        v.getTime ?
          new Date(v.getTime()) :
          clone(v) :
        v
  }

  return out
}

Tests

import assert from 'assert'

import { clone } from './clone'
import { equals } from './equals'

test('with array', () => {
  const arr = [
    {
      b : 2,
      c : 'foo',
      d : [ 1, 2, 3 ],
    },
    1,
    new Date(),
    null,
  ]
  expect(clone(arr)).toEqual(arr)
})

test('with object', () => {
  const arr = {
    a : 1,
    b : 2,
    c : 3,
    d : [ 1, 2, 3 ],
    e : new Date(),
  }
  expect(clone(arr)).toEqual(arr)
})

test('with date', () => {
  const date = new Date(
    2014, 10, 14, 23, 59, 59, 999
  )

  const cloned = clone(date)
  assert.notStrictEqual(date, cloned)
  expect(cloned).toEqual(new Date(
    2014, 10, 14, 23, 59, 59, 999
  ))

  expect(cloned.getDay()).toEqual(5)
})

test('with R.equals', () => {
  const objects = [ { a : 1 }, { b : 2 } ]

  const objectsClone = clone(objects)

  const result = [
    equals(objects, objectsClone),
    equals(objects[ 0 ], objectsClone[ 0 ]),
  ]
  expect(result).toEqual([ true, true ])
})

9 failed Ramda.clone specs

💥 Reason for the failure: rambda method work only with objects and arrays

var assert = require('assert');

var R = require('../../../../dist/rambda.js');
var eq = require('./shared/eq');
describe('deep clone integers, strings and booleans', function() {
  it('clones integers', function() {
    eq(R.clone(-4), -4);
    eq(R.clone(9007199254740991), 9007199254740991);
  });
  it('clones floats', function() {
    eq(R.clone(-4.5), -4.5);
    eq(R.clone(0.0), 0.0);
  });
  it('clones strings', function() {
    eq(R.clone('ramda'), 'ramda');
  });
  it('clones booleans', function() {
    eq(R.clone(true), true);
  });
});
describe('deep clone objects', function() {
  it('clones objects with circular references', function() {
    var x = {c: null};
    var y = {a: x};
    var z = {b: y};
    x.c = z;
    var clone = R.clone(x);
    assert.notStrictEqual(x, clone);
    assert.notStrictEqual(x.c, clone.c);
    assert.notStrictEqual(x.c.b, clone.c.b);
    assert.notStrictEqual(x.c.b.a, clone.c.b.a);
    assert.notStrictEqual(x.c.b.a.c, clone.c.b.a.c);
    eq(R.keys(clone), R.keys(x));
    eq(R.keys(clone.c), R.keys(x.c));
    eq(R.keys(clone.c.b), R.keys(x.c.b));
    eq(R.keys(clone.c.b.a), R.keys(x.c.b.a));
    eq(R.keys(clone.c.b.a.c), R.keys(x.c.b.a.c));
    x.c.b = 1;
    assert.notDeepEqual(clone.c.b, x.c.b);
  });
});
describe('deep clone arrays', function() {
});
describe('deep clone functions', function() {
});
describe('built-in types', function() {
  it('clones RegExp object', function() {
    R.forEach(function(pattern) {
      var clone = R.clone(pattern);
      assert.notStrictEqual(clone, pattern);
      eq(clone.constructor, RegExp);
      eq(clone.source, pattern.source);
      eq(clone.global, pattern.global);
      eq(clone.ignoreCase, pattern.ignoreCase);
      eq(clone.multiline, pattern.multiline);
    }, [/x/, /x/g, /x/i, /x/m, /x/gi, /x/gm, /x/im, /x/gim]);
  });
});
describe('deep clone deep nested mixed objects', function() {
  it('clones array with mutual ref object', function() {
    var obj = {a: 1};
    var list = [{b: obj}, {b: obj}];
    var clone = R.clone(list);
    assert.strictEqual(list[0].b, list[1].b);
    assert.strictEqual(clone[0].b, clone[1].b);
    assert.notStrictEqual(clone[0].b, list[0].b);
    assert.notStrictEqual(clone[1].b, list[1].b);
    eq(clone[0].b, {a:1});
    eq(clone[1].b, {a:1});
    obj.a = 2;
    eq(clone[0].b, {a:1});
    eq(clone[1].b, {a:1});
  });
});
describe('deep clone edge cases', function() {
  it('nulls, undefineds and empty objects and arrays', function() {
    eq(R.clone(null), null);
    eq(R.clone(undefined), undefined);
    assert.notStrictEqual(R.clone(undefined), null);
    var obj = {};
    assert.notStrictEqual(R.clone(obj), obj);
    var list = [];
    assert.notStrictEqual(R.clone(list), list);
  });
});
describe('Let `R.clone` use an arbitrary user defined `clone` method', function() {
  it('dispatches to `clone` method if present', function() {
    function ArbitraryClone(x) { this.value = x; }
    ArbitraryClone.prototype.clone = function() { return new ArbitraryClone(this.value); };
    var obj = new ArbitraryClone(42);
    var arbitraryClonedObj = R.clone(obj);
    eq(arbitraryClonedObj, new ArbitraryClone(42));
    eq(arbitraryClonedObj instanceof ArbitraryClone, true);
  });
});

compact

compact<T>(x: any[]): T[]

It returns a clone of list without the falsy or empty elements.

const list = [null, '', {}, [], 1]

const result = R.compact(list)
// => [1]

Try the above R.compact example in Rambda REPL

All Typescript definitions

compact<T>(x: any[]): T[];

R.compact source

import { equals } from './equals'
import { type } from './type'

const forbidden = [ 'Null', 'Undefined', 'RegExp' ]
const allowed = [ 'Number', 'Boolean' ]
const notEmpty = [ 'Array', 'String' ]

export function compact(list){
  const toReturn = []

  list.forEach(a => {
    const currentType = type(a)
    if (forbidden.includes(currentType)) return

    if (allowed.includes(currentType)) return toReturn.push(a)

    if (currentType === 'Object'){
      if (!equals(a, {})) toReturn.push(a)

      return
    }

    if (!notEmpty.includes(currentType)) return
    if (a.length === 0) return

    toReturn.push(a)
  })

  return toReturn
}

Tests

import { compact } from './compact'

test('happy', () => {
  const arr = [
    1,
    null,
    undefined,
    false,
    '',
    ' ',
    () => {},
    'foo',
    {},
    [],
    [ 1 ],
    /\s/g,
  ]

  const result = compact(arr)
  const expected = [ 1, false, ' ', 'foo', [ 1 ] ]

  expect(result).toEqual(expected)
})

Typescript test

import {compact} from 'rambda'

const list = ['', 2, 3]

describe('chain', () => {
  it('happy', () => {
    const result = compact(list)
    result // $ExpectType unknown[]
  })

  it('passing type', () => {
    const result = compact<number>(list)
    result // $ExpectType number[]
  })
})

complement

complement(pred: (...args: any[]) => boolean): (...args: any[]) => boolean

It returns inverted version of origin function that accept input as argument.

The return value of inverted is the negative boolean value of origin(input).

const origin = x => x > 5
const inverted = complement(origin)

const result = [
  origin(7),
  inverted(7)
] => [ true, false ]

Try the above R.complement example in Rambda REPL

All Typescript definitions

complement(pred: (...args: any[]) => boolean): (...args: any[]) => boolean;

R.complement source

export function complement(fn){
  return (...input) => !fn(...input)
}

Tests

import { complement } from './complement'

test('happy', () => {
  const fn = complement(x => x.length === 0)

  expect(fn([ 1, 2, 3 ])).toBeTrue()
})

test('with multiple parameters', () => {
  const between = function (
    a, b, c
  ){
    return a < b && b < c
  }
  const f = complement(between)
  expect(f(
    4, 5, 11
  )).toEqual(false)
  expect(f(
    12, 2, 6
  )).toEqual(true)
})

1 failed Ramda.complement specs

💥 Reason for the failure: ramda supports fantasy-land

var S = require('sanctuary');

var R = require('../../../../dist/rambda.js');
var eq = require('./shared/eq');
describe('complement', function() {
  it('accepts fantasy-land functors', function() {
    var Just = S.Just;
    var Nothing = S.Nothing;
    eq(R.complement(Just(true)), Just(false));
    eq(R.complement(Just(false)), Just(true));
    eq(R.complement(Nothing()), Nothing());
  });
});

compose

compose<T1>(fn0: () => T1): () => T1

It performs right-to-left function composition.

const result = R.compose(
  R.map(x => x * 2),
  R.filter(x => x > 2)
)([1, 2, 3, 4])

// => [6, 8]

Try the above R.compose example in Rambda REPL

All Typescript definitions

compose<T1>(fn0: () => T1): () => T1;
compose<V0, T1>(fn0: (x0: V0) => T1): (x0: V0) => T1;
compose<V0, V1, T1>(fn0: (x0: V0, x1: V1) => T1): (x0: V0, x1: V1) => T1;
compose<V0, V1, V2, T1>(fn0: (x0: V0, x1: V1, x2: V2) => T1): (x0: V0, x1: V1, x2: V2) => T1;

R.compose source

export function compose(...fns){
  if (fns.length === 0){
    throw new Error('compose requires at least one argument')
  }

  return (...args) => {
    const list = fns.slice()
    if (list.length > 0){
      const fn = list.pop()
      let result = fn(...args)
      while (list.length > 0){
        result = list.pop()(result)
      }

      return result
    }
  }
}

Tests

import { add } from './add'
import { compose } from './compose'
import { filter } from './filter'
import { last } from './last'
import { map } from './map'

test('happy', () => {
  const result = compose(
    last, map(add(10)), map(add(1))
  )([ 1, 2, 3 ])

  expect(result).toEqual(14)
})

test('accepts initially two arguments', () => {
  const result = compose(map(x => x * 2),
    (a, y) => filter(x => x > y, a))([ 1, 2, 3, 4 ], 2)

  expect(result).toEqual([ 6, 8 ])
})

test('when no arguments is passed', () => {
  expect(() => compose()).toThrow('compose requires at least one argument')
})

test('ramda spec', () => {
  const f = function (
    a, b, c
  ){
    return [ a, b, c ]
  }
  const g = compose(f)
  expect(g(
    1, 2, 3
  )).toEqual([ 1, 2, 3 ])
})

3 failed Ramda.compose specs

💥 Reason for the failure: ramda passes context to functions | rambda composed functions have no length

var assert = require('assert');
var jsv = require('jsverify');

var R = require('../../../../dist/rambda.js');
var eq = require('./shared/eq');
describe('compose', function() {
  it('performs right-to-left function composition', function() {
    //  f :: (String, Number?) -> ([Number] -> [Number])
    var f = R.compose(R.map, R.multiply, parseInt);
    eq(f.length, 2);
    eq(f('10')([1, 2, 3]), [10, 20, 30]);
    eq(f('10', 2)([1, 2, 3]), [2, 4, 6]);
  });
  it('passes context to functions', function() {
    function x(val) {
      return this.x * val;
    }
    function y(val) {
      return this.y * val;
    }
    function z(val) {
      return this.z * val;
    }
    var context = {
      a: R.compose(x, y, z),
      x: 4,
      y: 2,
      z: 1
    };
    eq(context.a(5), 40);
  });
  it('can be applied to one argument', function() {
    var f = function(a, b, c) { return [a, b, c]; };
    var g = R.compose(f);
    eq(g.length, 3);
    eq(g(1, 2, 3), [1, 2, 3]);
  });
});
describe('compose properties', function() {
  jsv.property('composes two functions', jsv.fn(), jsv.fn(), jsv.nat, function(f, g, x) {
    return R.equals(R.compose(f, g)(x), f(g(x)));
  jsv.property('associative',  jsv.fn(), jsv.fn(), jsv.fn(), jsv.nat, function(f, g, h, x) {
    var result = f(g(h(x)));
    return R.all(R.equals(result), [
      R.compose(f, g, h)(x),
      R.compose(f, R.compose(g, h))(x),
      R.compose(R.compose(f, g), h)(x)
    ]);
});

composeAsync

composeAsync<Out>(
  ...fns: (Async<any> | Func<any>)[]
): (input: any) => Promise<Out>

Asynchronous version of R.compose

const add = async x => {
  await R.delay(500)
  return x + 1
}
const passOn = async x => fn(x)

const result = R.composeAsync(
  add,
  passOn
)(0)
// `result` resolves to `2`

Try the above R.composeAsync example in Rambda REPL

All Typescript definitions

composeAsync<Out>(
  ...fns: (Async<any> | Func<any>)[]
): (input: any) => Promise<Out>;
composeAsync<Out>(
  ...fns: (Async<any> | Func<any>)[]
): (input: any) => Promise<Out>;

R.composeAsync source

import { type } from './type'

export function composeAsync(...inputArguments){
  return async function (startArgument){
    let argumentsToPass = startArgument

    while (inputArguments.length !== 0){
      const fn = inputArguments.pop()
      const typeFn = type(fn)

      if (typeFn === 'Async'){
        argumentsToPass = await fn(argumentsToPass)
      } else {
        argumentsToPass = fn(argumentsToPass)
      }
    }

    return argumentsToPass
  }
}

Tests

import { composeAsync } from './composeAsync'
import { delay as delayModule } from './delay'
import { equals } from './equals'
import { map } from './map'
import { mapAsync } from './mapAsync'
import { prop } from './prop'
import { tapAsync } from './tapAsync'

test('1', async () => {
  const fn = input =>
    new Promise(resolve => {
      setTimeout(() => {
        resolve({
          type    : 'result',
          payload : input,
        })
      }, 100)
    })

  const list = [ 'foo', 'bar' ].map(a => fn(a))

  const result = await composeAsync(
    map(prop('payload')),
    async inputs => Promise.all(inputs.map(async input => fn(input))),
    map(prop('payload'))
  )(await Promise.all(list))

  expect(result).toEqual([ 'foo', 'bar' ])
})

test('2', async () => {
  const delay = ms =>
    new Promise(resolve => {
      setTimeout(() => {
        resolve(ms + 110)
      }, ms)
    })

  const delayAsync = async ms => delay(ms)

  const result = await composeAsync(
    a => a - 1000,
    a => a,
    async a => delayAsync(a),
    a => a + 11
  )(await delay(20))
  expect(result).toEqual(-749)
})

test('3', async () => {
  try {
    const delay = ms =>
      new Promise((_, reject) => {
        setTimeout(() => {
          reject('error')
        }, ms)
      })

    const delayAsync = async ms => delay(ms)

    await composeAsync(a => a - 1000, delayAsync)(20)
  } catch (err){
    expect(err).toEqual('error')
  }
})

test('4', async () => {
  let sideEffect
  const result = await composeAsync(tapAsync(async x => {
    sideEffect = equals(x, [ 2, 4, 6 ])

    return delayModule(x * 3)
  }),
  mapAsync(async x => {
    await delayModule(x * 100)

    return x * 2
  }))([ 1, 2, 3 ])

  expect(result).toEqual([ 2, 4, 6 ])

  expect(sideEffect).toEqual(true)
})

test('inside compose explicit `async` keyword', async () => {
  const delay = ms =>
    new Promise((res, rej) => {
      const b = ms + 7

      res(b)
    })

  const result = await composeAsync(
    a => a,
    a => a + 1000,
    async a => delay(a),
    a => a + 11
  )(20)

  expect(result).toEqual(1038)
})

const delayFn = ms =>
  new Promise((res, rej) => {
    const b = ms + 7

    res(b)
  })

test('known issue - function returning promise', async () => {
  const result = await composeAsync(
    a => a,
    a => a + 1000,
    delayFn,
    a => a + 11
  )(20)

  expect(result).toEqual('[object Promise]1000')
})

test('throw error', async () => {
  const delay = async () => {
    await delayFn(1)
    JSON.parse('{foo')
  }

  let flag = true
  try {
    await composeAsync(
      a => a,
      a => a + 1000,
      async () => delay(),
      a => a + 11
    )(20)
  } catch (e){
    flag = false
  }

  expect(flag).toBe(false)
})

concat

concat<T>(x: ReadonlyArray<T>, y: ReadonlyArray<T>): T[]

It returns a new string or array, which is the result of merging x and y.

R.concat([1, 2])([3, 4]) // => [1, 2, 3, 4]
R.concat('foo', 'bar') // => 'foobar'

Try the above R.concat example in Rambda REPL

All Typescript definitions

concat<T>(x: ReadonlyArray<T>, y: ReadonlyArray<T>): T[];
concat<T>(x: ReadonlyArray<T>): (y: ReadonlyArray<T>) => T[];
concat(x: string, y: string): string;
concat(x: string): (y: string) => string;

R.concat source

export function concat(x, y){
  if (arguments.length === 1) return _y => concat(x, _y)

  return typeof x === 'string' ? `${ x }${ y }` : [ ...x, ...y ]
}

Tests

import { concat } from './concat'

test('happy', () => {
  const arr1 = [ 'a', 'b', 'c' ]
  const arr2 = [ 'd', 'e', 'f' ]

  const a = concat(arr1, arr2)
  const b = concat(arr1)(arr2)
  const expectedResult = [ 'a', 'b', 'c', 'd', 'e', 'f' ]

  expect(a).toEqual(expectedResult)
  expect(b).toEqual(expectedResult)
})

test('with strings', () => {
  expect(concat('ABC', 'DEF')).toEqual('ABCDEF')
})

1 failed Ramda.concat specs

💥 Reason for the failure: ramda pass to concat method if present

var assert = require('assert');

var R = require('../../../../dist/rambda.js');
var eq = require('./shared/eq');
describe('concat', function() {
  var z1 = {
    x: 'z1',
    concat: function(that) { return this.x + ' ' + that.x; }
  };
  var z2 = {
    x: 'z2'
  };
  it('delegates to non-String object with a concat method, as second param', function() {
    eq(R.concat(z1, z2), 'z1 z2');
  });
});

cond

cond(conditions: [Pred, (...a: readonly any[]) => any][]): (...a: readonly any[]) => any

It takes list with conditions and returns a new function fn that expects input as argument.

This function will start evaluating the conditions in order to find the first winner(order of conditions matter).

The winner is this condition, which left side returns true when input is its argument. Then the evaluation of the right side of the winner will be the final result.

If no winner is found, then fn returns undefined.

const fn = R.cond([
  [ x => x > 25, R.always('more than 25') ],
  [ x => x > 15, R.always('more than 15') ],
  [ R.T, x => `${x} is nothing special` ],
])

const result = [
  fn(30),
  fn(20),
  fn(10),
] 
// => ['more than 25', 'more than 15', '10 is nothing special']

Try the above R.cond example in Rambda REPL

All Typescript definitions

cond(conditions: [Pred, (...a: readonly any[]) => any][]): (...a: readonly any[]) => any;
cond<A, B>(conditions: [SafePred<A>, (...a: readonly A[]) => B][]): (...a: readonly A[]) => B;

R.cond source

export function cond(conditions){
  return input => {
    let done = false
    let toReturn
    conditions.forEach(([ predicate, resultClosure ]) => {
      if (!done && predicate(input)){
        done = true
        toReturn = resultClosure(input)
      }
    })

    return toReturn
  }
}

Tests

import { always } from './always'
import { cond } from './cond'
import { equals } from './equals'
import { T } from './T'

test('returns a function', () => {
  expect(typeof cond([])).toEqual('function')
})

test('returns a conditional function', () => {
  const fn = cond([
    [ equals(0), always('water freezes at 0°C') ],
    [ equals(100), always('water boils at 100°C') ],
    [
      T,
      function (temp){
        return 'nothing special happens at ' + temp + '°C'
      },
    ],
  ])
  expect(fn(0)).toEqual('water freezes at 0°C')
  expect(fn(50)).toEqual('nothing special happens at 50°C')
  expect(fn(100)).toEqual('water boils at 100°C')
})

test('no winner', () => {
  const fn = cond([
    [ equals('foo'), always(1) ],
    [ equals('bar'), always(2) ],
  ])
  expect(fn('quux')).toEqual(undefined)
})

test('predicates are tested in order', () => {
  const fn = cond([
    [ T, always('foo') ],
    [ T, always('bar') ],
    [ T, always('baz') ],
  ])
  expect(fn()).toEqual('foo')
})

Typescript test

import {cond, always, equals} from 'rambda'

describe('cond', () => {
  it('happy', () => {
    const fn = cond<number, string>([
      [equals(0), always('water freezes at 0°C')],
      [equals(100), always('water boils at 100°C')],
      [
        () => true,
        function(temp) {
          return 'nothing special happens at ' + temp + '°C'
        },
      ],
    ])

    const a = fn(0)
    a // $ExpectType string
  })
})

2 failed Ramda.cond specs

💥 Reason for the failure: pass to transformer is not applied in rambda

var R = require('../../../../dist/rambda.js');
var eq = require('./shared/eq');

describe('cond', function() {
  it('forwards all arguments to predicates and to transformers', function() {
    var fn = R.cond([
      [function(_, x) { return x === 42; }, function() { return arguments.length; }]
    ]);
    eq(fn(21, 42, 84), 3);
  });
  it('retains highest predicate arity', function() {
    var fn = R.cond([
      [R.nAry(2, R.T), R.T],
      [R.nAry(3, R.T), R.T],
      [R.nAry(1, R.T), R.T]
    ]);
    eq(fn.length, 3);
  });
});

converge

converge(after: ((...a: readonly any[]) => any), fns: Array<((...a: readonly any[]) => any)>): (...a: readonly any[]) => any

All Typescript definitions

converge(after: ((...a: readonly any[]) => any), fns: Array<((...a: readonly any[]) => any)>): (...a: readonly any[]) => any;

R.converge source

import { curryN } from './curryN'
import { map } from './map'
import { max } from './max'
import { reduce } from './reduce'

export function converge(fn, transformers){
  if (arguments.length === 1)
    return _transformers => converge(fn, _transformers)

  const highestArity = reduce(
    (a, b) => max(a, b.length), 0, transformers
  )

  return curryN(highestArity, function (){
    return fn.apply(this,
      map(g => g.apply(this, arguments), transformers))
  })
}

Tests

import { add } from './add'
import { converge } from './converge'

const mult = function (a, b){
  return a * b
}

const f1 = converge(mult, [
  function (a){
    return a
  },
  function (a){
    return a
  },
])
const f2 = converge(mult, [
  function (a){
    return a
  },
  function (a, b){
    return b
  },
])
const f3 = converge(mult, [
  function (a){
    return a
  },
  function (
    a, b, c
  ){
    return c
  },
])

test('passes the results of applying the arguments individually to two separate functions into a single one', () => {
  expect(converge(mult, [ add(1), add(3) ])(2)).toEqual(15) // mult(add1(2), add3(2)) = mult(3, 5) = 3 * 15;
})

test('returns a function with the length of the "longest" argument', () => {
  expect(f1.length).toEqual(1)
  expect(f2.length).toEqual(2)
  expect(f3.length).toEqual(3)
})

test('passes context to its functions', () => {
  const a = function (x){
    return this.f1(x)
  }
  const b = function (x){
    return this.f2(x)
  }
  const c = function (x, y){
    return this.f3(x, y)
  }
  const d = converge(c, [ a, b ])
  const context = {
    f1 : add(1),
    f2 : add(2),
    f3 : add,
  }
  expect(a.call(context, 1)).toEqual(2)
  expect(b.call(context, 1)).toEqual(3)
  expect(d.call(context, 1)).toEqual(5)
})

test('returns a curried function', () => {
  expect(f2(6)(7)).toEqual(42)
  expect(f3().length).toEqual(3)
})

test('works with empty functions list', () => {
  const fn = converge(function (){
    return arguments.length
  }, [])
  expect(fn.length).toEqual(0)
  expect(fn()).toEqual(0)
})

count

count<T>(searchFor: T, list: any[]): number

It counts how many times searchFor is within list according to R.equals.

const list = [1, {a:1}, 1, 'foo']
const searchFor = 1

const result = R.count(searchFor, list)
// => 2

Try the above R.count example in Rambda REPL

All Typescript definitions

count<T>(searchFor: T, list: any[]): number;
count<T>(searchFor: T): (list: any[]) => number;

R.count source

import { _isArray } from './_internals/_isArray'
import { equals } from './equals'

export function count(searchFor, list){
  if (arguments.length === 1){
    return listHolder => count(searchFor, listHolder)
  }
  if (!_isArray(list)) return 0

  return list.filter(x => equals(x, searchFor)).length
}

Tests

import { count } from './count'

test('when 0', () => {
  const target = { a : 1 }
  const list = []

  const result = count(target, list)
  const expectedResult = 0

  expect(result).toEqual(expectedResult)
})

test('when 2', () => {
  const target = { a : 1 }
  const list = [ 2, 1, 2, { a : 1 }, 22, { a : 1 } ]

  const result = count(target)(list)
  const expectedResult = 2

  expect(result).toEqual(expectedResult)
})

curry

curry<F extends (...args: any) => any>(f: F): FunctionToolbelt.Curry<F>

It expects a function as input and returns its curried version.

const fn = (a, b, c) => a + b + c
const curried = R.curry(fn)
const sum = curried(1,2)

const result = sum(3) // => 6

Try the above R.curry example in Rambda REPL

All Typescript definitions

curry<F extends (...args: any) => any>(f: F): FunctionToolbelt.Curry<F>;

R.curry source

import { curryN } from './curryN'

export function curry(fn){
  return curryN(fn.length, fn)
}

Tests

import { curry } from './curry'

test('happy', () => {
  const addFourNumbers = (
    a, b, c, d
  ) => a + b + c + d
  const curriedAddFourNumbers = curry(addFourNumbers)
  const f = curriedAddFourNumbers(1, 2)
  const g = f(3)

  expect(g(4)).toEqual(10)
})

test('when called with more arguments', () => {
  const add = curry((n, n2) => n + n2)

  expect(add(
    1, 2, 3
  )).toEqual(3)
})

test('when called with zero arguments', () => {
  const sub = curry((a, b) => a - b)
  const s0 = sub()

  expect(s0(5, 2)).toEqual(3)
})

test('when called via multiple curry stages', () => {
  const join = curry((
    a, b, c, d
  ) => [ a, b, c, d ].join('-'))

  const stage1 = join('A')
  const stage2 = stage1('B', 'C')

  expect(stage2('D')).toEqual('A-B-C-D')
})

3 failed Ramda.curry specs

💥 Reason for the failure: ramda support placeholder(R.__)

var R = require('../../../../dist/rambda.js');
var eq = require('./shared/eq');
var jsv = require('jsverify');
var funcN = require('./shared/funcN');

describe('curry', function() {
  it('properly reports the length of the curried function', function() {
    var f = R.curry(function(a, b, c, d) {return (a + b * c) / d;});
    eq(f.length, 4);
    var g = f(12);
    eq(g.length, 3);
    var h = g(3);
    eq(h.length, 2);
    eq(g(3, 6).length, 1);
  });
  it('preserves context', function() {
    var ctx = {x: 10};
    var f = function(a, b) { return a + b * this.x; };
    var g = R.curry(f);
    eq(g.call(ctx, 2, 4), 42);
    eq(g.call(ctx, 2).call(ctx, 4), 42);
  });
  it('supports R.__ placeholder', function() {
    var f = function(a, b, c) { return [a, b, c]; };
    var g = R.curry(f);
    var _ = R.__;
    eq(g(1)(2)(3), [1, 2, 3]);
    eq(g(1)(2, 3), [1, 2, 3]);
    eq(g(1, 2)(3), [1, 2, 3]);
    eq(g(1, 2, 3), [1, 2, 3]);
    eq(g(_, 2, 3)(1), [1, 2, 3]);
    eq(g(1, _, 3)(2), [1, 2, 3]);
    eq(g(1, 2, _)(3), [1, 2, 3]);
    eq(g(1, _, _)(2)(3), [1, 2, 3]);
    eq(g(_, 2, _)(1)(3), [1, 2, 3]);
    eq(g(_, _, 3)(1)(2), [1, 2, 3]);
    eq(g(1, _, _)(2, 3), [1, 2, 3]);
    eq(g(_, 2, _)(1, 3), [1, 2, 3]);
    eq(g(_, _, 3)(1, 2), [1, 2, 3]);
    eq(g(1, _, _)(_, 3)(2), [1, 2, 3]);
    eq(g(_, 2, _)(_, 3)(1), [1, 2, 3]);
    eq(g(_, _, 3)(_, 2)(1), [1, 2, 3]);
    eq(g(_, _, _)(_, _)(_)(1, 2, 3), [1, 2, 3]);
    eq(g(_, _, _)(1, _, _)(_, _)(2, _)(_)(3), [1, 2, 3]);
  });
  it('supports @@functional/placeholder', function() {
    var f = function(a, b, c) { return [a, b, c]; };
    var g = R.curry(f);
    var _ = {'@@functional/placeholder': true, x: Math.random()};
    eq(g(1)(2)(3), [1, 2, 3]);
    eq(g(1)(2, 3), [1, 2, 3]);
    eq(g(1, 2)(3), [1, 2, 3]);
    eq(g(1, 2, 3), [1, 2, 3]);
    eq(g(_, 2, 3)(1), [1, 2, 3]);
    eq(g(1, _, 3)(2), [1, 2, 3]);
    eq(g(1, 2, _)(3), [1, 2, 3]);
    eq(g(1, _, _)(2)(3), [1, 2, 3]);
    eq(g(_, 2, _)(1)(3), [1, 2, 3]);
    eq(g(_, _, 3)(1)(2), [1, 2, 3]);
    eq(g(1, _, _)(2, 3), [1, 2, 3]);
    eq(g(_, 2, _)(1, 3), [1, 2, 3]);
    eq(g(_, _, 3)(1, 2), [1, 2, 3]);
    eq(g(1, _, _)(_, 3)(2), [1, 2, 3]);
    eq(g(_, 2, _)(_, 3)(1), [1, 2, 3]);
    eq(g(_, _, 3)(_, 2)(1), [1, 2, 3]);
    eq(g(_, _, _)(_, _)(_)(1, 2, 3), [1, 2, 3]);
    eq(g(_, _, _)(1, _, _)(_, _)(2, _)(_)(3), [1, 2, 3]);
  });
});
describe('curry properties', function() {
  jsv.property('curries multiple values', funcN(4), jsv.json, jsv.json, jsv.json, jsv.json, function(f, a, b, c, d) {
    var g = R.curry(f);
    return R.all(R.equals(f(a, b, c, d)), [
      g(a, b, c, d),
      g(a)(b)(c)(d),
      g(a)(b, c, d),
      g(a, b)(c, d),
      g(a, b, c)(d)
    ]);
  jsv.property('curries with placeholder', funcN(3), jsv.json, jsv.json, jsv.json, function(f, a, b, c) {
    var _ = {'@@functional/placeholder': true, x: Math.random()};
    var g = R.curry(f);
    return R.all(R.equals(f(a, b, c)), [
      g(_, _, c)(a, b),
      g(a, _, c)(b),
      g(_, b, c)(a),
      g(a, _, _)(_, c)(b),
      g(a, b, _)(c)
    ]);
});

curryN

curryN(length: number, fn: (...args: readonly any[]) => any): (...a: readonly any[]) => any

It returns a curried equivalent of the provided function, with the specified arity.

All Typescript definitions

curryN(length: number, fn: (...args: readonly any[]) => any): (...a: readonly any[]) => any;

R.curryN source

function _curryN(
  n, cache, fn
){
  return function (){
    // concat cache and the arguments as fast as possible https://jsperf.com/concat-two-arrays-quickly
    let ci = 0
    let ai = 0
    const cl = cache.length
    const al = arguments.length
    const args = new Array(cl + al)
    while (ci < cl){
      args[ ci ] = cache[ ci ]
      ci++
    }
    while (ai < al){
      args[ cl + ai ] = arguments[ ai ]
      ai++
    }
    const remaining = n - args.length

    return args.length >= n ?
      fn.apply(this, args) :
      _arity(remaining, _curryN(
        n, args, fn
      ))
  }
}

function _arity(n, fn){
  switch (n){
  case 0:
    return function (){
      return fn.apply(this, arguments)
    }
  case 1:
    return function (_1){
      return fn.apply(this, arguments)
    }
  case 2:
    return function (_1, _2){
      return fn.apply(this, arguments)
    }
  case 3:
    return function (
      _1, _2, _3
    ){
      return fn.apply(this, arguments)
    }
  case 4:
    return function (
      _1, _2, _3, _4
    ){
      return fn.apply(this, arguments)
    }
  case 5:
    return function (
      _1, _2, _3, _4, _5
    ){
      return fn.apply(this, arguments)
    }
  case 6:
    return function (
      _1, _2, _3, _4, _5, _6
    ){
      return fn.apply(this, arguments)
    }
  case 7:
    return function (
      _1, _2, _3, _4, _5, _6, _7
    ){
      return fn.apply(this, arguments)
    }
  case 8:
    return function (
      _1, _2, _3, _4, _5, _6, _7, _8
    ){
      return fn.apply(this, arguments)
    }
  case 9:
    return function (
      _1, _2, _3, _4, _5, _6, _7, _8, _9
    ){
      return fn.apply(this, arguments)
    }
  case 10:
    return function (
      _1, _2, _3, _4, _5, _6, _7, _8, _9, _10
    ){
      return fn.apply(this, arguments)
    }
  default:
    throw new Error('First argument to _arity must be a non-negative integer no greater than ten')
  }
}

export function curryN(n, fn){
  if (arguments.length === 1) return _fn => curryN(n, _fn)

  return _arity(n, _curryN(
    n, [], fn
  ))
}

Tests

import { curryN } from './curryN'

describe('curryN', () => {
  function source(
    a, b, c, d
  ){
    void d

    return a * b * c
  }

  it('accepts an arity', () => {
    const curried = curryN(3, source)
    expect(curried(1)(2)(3)).toEqual(6)
    expect(curried(1, 2)(3)).toEqual(6)
    expect(curried(1)(2, 3)).toEqual(6)
    expect(curried(
      1, 2, 3
    )).toEqual(6)
  })

  it('can be partially applied', () => {
    const curry3 = curryN(3)
    const curried = curry3(source)
    expect(curried.length).toEqual(3)
    expect(curried(1)(2)(3)).toEqual(6)
    expect(curried(1, 2)(3)).toEqual(6)
    expect(curried(1)(2, 3)).toEqual(6)
    expect(curried(
      1, 2, 3
    )).toEqual(6)
  })

  it('preserves context', () => {
    const ctx = { x : 10 }
    const f = function (a, b){
      return a + b * this.x
    }
    const g = curryN(2, f)

    expect(g.call(
      ctx, 2, 4
    )).toEqual(42)
    expect(g.call(ctx, 2).call(ctx, 4)).toEqual(42)
  })

  it('forwards extra arguments', () => {
    const f = function (){
      return Array.prototype.slice.call(arguments)
    }
    const g = curryN(3, f)

    expect(g(
      1, 2, 3
    )).toEqual([ 1, 2, 3 ])
    expect(g(
      1, 2, 3, 4
    )).toEqual([ 1, 2, 3, 4 ])
    expect(g(1, 2)(3, 4)).toEqual([ 1, 2, 3, 4 ])
    expect(g(1)(
      2, 3, 4
    )).toEqual([ 1, 2, 3, 4 ])
    expect(g(1)(2)(3, 4)).toEqual([ 1, 2, 3, 4 ])
  })
})

debounce

debounce<T>(fn: T, ms: number): (input: T) => T

It creates a debounced function that delays invoking fn until after wait milliseconds ms have elapsed since the last time the debounced function was invoked.

let counter = 0
const increment = () => {
  counter++
}

const debounced = R.debounce(increment, 1000)

const result = async function(){
  debounced()
  await R.delay(500)
  debounced()
  await R.delay(800)
  console.log(counter) // => 0

  await R.delay(1200)
  console.log(counter) // => 1

  return counter
}
// `result` resolves to `1`

Try the above R.debounce example in Rambda REPL

All Typescript definitions

debounce<T>(fn: T, ms: number): (input: T) => T;

R.debounce source

export function debounce(
  func, ms, immediate = false
){
  let timeout

  return function (...input){
    const later = function (){
      timeout = null
      if (!immediate){
        func.apply(null, input)
      }
    }
    const callNow = immediate && !timeout
    clearTimeout(timeout)
    timeout = setTimeout(later, ms)
    if (callNow){
      func.apply(null, input)
    }
  }
}

Tests

import { debounce } from './debounce'
import { delay } from './delay'

test('', async () => {
  let counter = 0
  let aHolder
  let bHolder

  const inc = (a, b) => {
    aHolder = a
    bHolder = b
    counter++
  }
  const incWrapped = debounce(inc, 500)

  incWrapped(1, 2)
  expect(counter).toBe(0)
  expect(aHolder).toBe(undefined)
  expect(bHolder).toBe(undefined)

  await delay(200)

  incWrapped(2, 3)
  expect(counter).toBe(0)

  await delay(200)

  incWrapped(3, 4)
  expect(counter).toBe(0)
  expect(aHolder).toBe(undefined)
  expect(bHolder).toBe(undefined)

  await delay(200)
  incWrapped(5, 6)
  expect(counter).toBe(0)

  await delay(700)
  expect(counter).toBe(1)
  expect(aHolder).toBe(5)
  expect(bHolder).toBe(6)
})

test('immediate debounce', async () => {
  let counter = 0
  const inc = () => {
    counter++
  }

  const incWrapped = debounce(
    inc, 500, true
  )
  incWrapped()
  expect(counter).toBe(1)
  await delay(200)
  incWrapped()
  expect(counter).toBe(1)
  await delay(200)
  incWrapped()
  expect(counter).toBe(1)
  await delay(700)
  incWrapped()
  expect(counter).toBe(2)
})

dec

dec(x: number): number

It decrements a number.

All Typescript definitions

dec(x: number): number;

R.dec source

export const dec = x => x - 1

Tests

import { dec } from './dec'

test('happy', () => {
  expect(dec(2)).toBe(1)
})

defaultTo

defaultTo<T>(defaultValue: T): (...inputArguments: (T | null | undefined)[]) => T

It returns defaultValue, if all of inputArguments are undefined, null or NaN.

Else, it returns the first truthy inputArguments instance(from left to right).

// With single input argument
R.defaultTo('foo', 'bar') // => 'bar'
R.defaultTo('foo', undefined) // => 'foo'

// With multiple input arguments
R.defaultTo('foo', undefined, null, NaN) // => 'foo'
R.defaultTo('foo', undefined, 'bar', NaN, 'qux') // => 'bar'
R.defaultTo('foo', undefined, null, NaN, 'quz') // => 'qux'

Try the above R.defaultTo example in Rambda REPL

All Typescript definitions

defaultTo<T>(defaultValue: T): (...inputArguments: (T | null | undefined)[]) => T;
defaultTo<T>(defaultValue: T, ...inputArguments: (T | null | undefined)[]): T;
defaultTo<T, U>(defaultValue: T | U, ...inputArguments: (T | U | null | undefined)[]): T | U;

R.defaultTo source

function flagIs(inputArguments){
  return (
    inputArguments === undefined ||
    inputArguments === null ||
    Number.isNaN(inputArguments) === true
  )
}

export function defaultTo(defaultArgument, ...inputArguments){
  if (arguments.length === 1){
    return _inputArguments => defaultTo(defaultArgument, _inputArguments)
  } else if (arguments.length === 2){
    return flagIs(inputArguments[ 0 ]) ? defaultArgument : inputArguments[ 0 ]
  }

  const limit = inputArguments.length - 1
  let len = limit + 1
  let ready = false
  let holder

  while (!ready){
    const instance = inputArguments[ limit - len + 1 ]

    if (len === 0){
      ready = true
    } else if (flagIs(instance)){
      len -= 1
    } else {
      holder = instance
      ready = true
    }
  }

  return holder === undefined ? defaultArgument : holder
}

Tests

import { defaultTo } from './defaultTo'

test('with undefined', () => {
  expect(defaultTo('foo')(undefined)).toEqual('foo')
})

test('with null', () => {
  expect(defaultTo('foo')(null)).toEqual('foo')
})

test('with NaN', () => {
  expect(defaultTo('foo')(NaN)).toEqual('foo')
})

test('with empty string', () => {
  expect(defaultTo('foo', '')).toEqual('')
})

test('with false', () => {
  expect(defaultTo('foo', false)).toEqual(false)
})

test('when inputArgument passes initial check', () => {
  expect(defaultTo('foo', 'bar')).toEqual('bar')
})

test('default extends to indefinite input arguments - case 1', () => {
  const result = defaultTo(
    'foo', null, 'bar'
  )
  const expected = 'bar'

  expect(result).toEqual(expected)
})

test('default extends to indefinite input arguments - case 2', () => {
  const result = defaultTo(
    'foo', null, NaN, 'bar'
  )
  const expected = 'bar'

  expect(result).toEqual(expected)
})

test('default extends to indefinite input arguments - case 3', () => {
  const result = defaultTo(
    'foo', null, NaN, undefined
  )
  const expected = 'foo'

  expect(result).toEqual(expected)
})

test('default extends to indefinite input arguments - case 4', () => {
  const result = defaultTo(
    'foo', null, NaN, undefined, 'bar'
  )
  const expected = 'bar'

  expect(result).toEqual(expected)
})

test('default extends to indefinite input arguments - case 5', () => {
  const result = defaultTo(
    'foo', null, NaN, 'bar', 'baz'
  )
  const expected = 'bar'

  expect(result).toEqual(expected)
})

test('default extends to indefinite input arguments - case 6', () => {
  const result = defaultTo(
    'foo', null, NaN, undefined, null, NaN
  )
  const expected = 'foo'

  expect(result).toEqual(expected)
})

Typescript test

import {defaultTo} from 'rambda'

describe('defaultTo with Ramda spec', () => {
  it('happy', () => {
    const x = defaultTo<string>('foo', undefined) // $ExpectType string
    x // $ExpectType string
  })
  it('fallback', () => {
    const x = defaultTo('foo', undefined) // $ExpectType "foo"
    x // $ExpectType "foo"
    const y = defaultTo('foo', 'bar') // $ExpectType "foo" | "bar"
    y // $ExpectType "foo" | "bar"
  })
  it('with one type', () => {
    const x = defaultTo<string>('foo', 'bar') // $ExpectType string
    x // $ExpectType string
  })
  it('with two types', () => {
    const x = defaultTo<string, number>('foo', 1) // $ExpectType string | number
    x // $ExpectType string | number
  })
})

describe('defaultTo with Rambda spec', () => {
  it('happy', () => {
    const x = defaultTo<string>('foo', undefined, 'bar') // $ExpectType string
    x // $ExpectType string
  })

  it('happy with curry', () => {
    const fn = defaultTo<string>('foo')
    const x = fn(undefined, 'bar', null) // $ExpectType string
    x // $ExpectType string
    const y = fn(undefined) // $ExpectType string
    y // $ExpectType string
  })

  it('with two types', () => {
    const x = defaultTo<string, number>('foo', undefined, 1, null, 2, 'bar') // $ExpectType string | number
    x // $ExpectType string | number
  })
})

delay

delay(ms: number): Promise<'RAMBDAX_DELAY'>

setTimeout as a promise that resolves to R.DELAY variable after ms milliseconds.

const result = R.delay(1000)
// `result` resolves to `RAMBDAX_DELAY`

Try the above R.delay example in Rambda REPL

All Typescript definitions

delay(ms: number): Promise<'RAMBDAX_DELAY'>;

R.delay source

export const DELAY = 'RAMBDAX_DELAY'

export function delay(ms){
  return new Promise(resolve => {
    setTimeout(() => {
      resolve(DELAY)
    }, ms)
  })
}

Tests

import { DELAY, delay } from './delay'

test('usage with variables', async () => {
  expect(await delay(500)).toBe(DELAY)
})

Typescript test

import {delay, DELAY} from 'rambda'

describe('R.delay', () => {
  it('happy', async() => {
    const result = await delay(100)
    result // $ExpectType "RAMBDAX_DELAY"
    DELAY // $ExpectType "RAMBDAX_DELAY"
  })
})

difference

difference<T>(a: ReadonlyArray<T>, b: ReadonlyArray<T>): T[]

It returns the uniq set of all elements in the first list a not contained in the second list b.

const a = [ 1, 2, 3, 4 ]
const b = [ 3, 4, 5, 6 ]

const result = difference(a, b)
// => [ 1, 2 ]

Try the above R.difference example in Rambda REPL

All Typescript definitions

difference<T>(a: ReadonlyArray<T>, b: ReadonlyArray<T>): T[];
difference<T>(a: ReadonlyArray<T>): (b: ReadonlyArray<T>) => T[];

R.difference source

import { includes } from './includes'
import { uniq } from './uniq'

export function difference(a, b){
  if (arguments.length === 1) return _b => difference(a, _b)

  return uniq(a).filter(aInstance => !includes(aInstance, b))
}

Tests

import { difference } from './difference'

test('difference', () => {
  const a = [ 1, 2, 3, 4 ]
  const b = [ 3, 4, 5, 6 ]
  expect(difference(a)(b)).toEqual([ 1, 2 ])

  expect(difference([], [])).toEqual([])
})

test('difference with objects', () => {
  const a = [ { id : 1 }, { id : 2 }, { id : 3 }, { id : 4 } ]
  const b = [ { id : 3 }, { id : 4 }, { id : 5 }, { id : 6 } ]
  expect(difference(a, b)).toEqual([ { id : 1 }, { id : 2 } ])
})

test('no duplicates in first list', () => {
  const M2 = [ 1, 2, 3, 4, 1, 2, 3, 4 ]
  const N2 = [ 3, 3, 4, 4, 5, 5, 6, 6 ]
  expect(difference(M2, N2)).toEqual([ 1, 2 ])
})

test('should use R.equals', () => {
  expect(difference([ NaN ], [ NaN ]).length).toEqual(0)
})

1 failed Ramda.difference specs

💥 Reason for the failure: ramda supports negative zero

var R = require('../../../../dist/rambda.js');
var eq = require('./shared/eq');

describe('difference', function() {
  var M = [1, 2, 3, 4];
  var M2 = [1, 2, 3, 4, 1, 2, 3, 4];
  var N = [3, 4, 5, 6];
  var N2 = [3, 3, 4, 4, 5, 5, 6, 6];
  var Z = [3, 4, 5, 6, 10];
  var Z2 = [1, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 8];
  it('has R.equals semantics', function() {
    function Just(x) { this.value = x; }
    Just.prototype.equals = function(x) {
      return x instanceof Just && R.equals(x.value, this.value);
    };
    eq(R.difference([0], [-0]).length, 1);
    eq(R.difference([-0], [0]).length, 1);
    eq(R.difference([NaN], [NaN]).length, 0);
    eq(R.difference([new Just([42])], [new Just([42])]).length, 0);
  });
});

dissoc

dissoc<T>(prop: string, obj: any): T

It returns a new object that does not contain property prop.

R.dissoc('b', {a: 1, b: 2, c: 3})
//=> {a: 1, c: 3}

Try the above R.dissoc example in Rambda REPL

All Typescript definitions

dissoc<T>(prop: string, obj: any): T;
dissoc(prop: string): <U>(obj: any) => U;

R.dissoc source

export function dissoc(prop, obj){
  if (arguments.length === 1) return _obj => dissoc(prop, _obj)

  if (obj === null || obj === undefined) return {}

  const willReturn = {}
  for (const p in obj){
    willReturn[ p ] = obj[ p ]
  }
  delete willReturn[ prop ]

  return willReturn
}

Tests

import { dissoc } from './dissoc'

test('input is null or undefined', () => {
  expect(dissoc('b', null)).toEqual({})
  expect(dissoc('b', undefined)).toEqual({})
})

test('property exists curried', () => {
  expect(dissoc('b')({
    a : 1,
    b : 2,
  })).toEqual({ a : 1 })
})

test('property doesn\'t exists', () => {
  expect(dissoc('c', {
    a : 1,
    b : 2,
  })).toEqual({
    a : 1,
    b : 2,
  })
})

test('works with non-string property', () => {
  expect(dissoc(42, {
    a  : 1,
    42 : 2,
  })).toEqual({ a : 1 })

  expect(dissoc(null, {
    a    : 1,
    null : 2,
  })).toEqual({ a : 1 })

  expect(dissoc(undefined, {
    a         : 1,
    undefined : 2,
  })).toEqual({ a : 1 })
})

test('includes prototype properties', () => {
  function Rectangle(width, height){
    this.width = width
    this.height = height
  }
  const area = Rectangle.prototype.area = function (){
    return this.width * this.height
  }
  const rect = new Rectangle(7, 6)

  expect(dissoc('area', rect)).toEqual({
    width  : 7,
    height : 6,
  })

  expect(dissoc('width', rect)).toEqual({
    height : 6,
    area   : area,
  })

  expect(dissoc('depth', rect)).toEqual({
    width  : 7,
    height : 6,
    area   : area,
  })
})

divide

divide(a: number, b: number): number

R.divide(71, 100) // => 0.71

Try the above R.divide example in Rambda REPL

All Typescript definitions

divide(a: number, b: number): number;
divide(a: number): (b: number) => number;

R.divide source

export function divide(a, b){
  if (arguments.length === 1) return _b => divide(a, _b)

  return a / b
}

Tests

import { divide } from './divide'

test('happy', () => {
  expect(divide(71, 100)).toEqual(0.71)
  expect(divide(71)(100)).toEqual(0.71)
})

drop

drop<T>(howManyToDrop: number, listOrString: ReadonlyArray<T>): T[]

It returns listOrString with howManyToDrop items dropped from its beginning.

R.drop(2, ['foo', 'bar', 'baz']) // => ['baz']
R.drop(2, 'foobar')  // => 'obar'

Try the above R.drop example in Rambda REPL

All Typescript definitions

drop<T>(howManyToDrop: number, listOrString: ReadonlyArray<T>): T[];
drop(howManyToDrop: number, listOrString: string): string;
drop<T>(howManyToDrop: number): {
  (listOrString: string): string;
  (listOrString: ReadonlyArray<T>): T[];
};

R.drop source

export function drop(howManyToDrop, listOrString){
  if (arguments.length === 1) return _list => drop(howManyToDrop, _list)

  return listOrString.slice(howManyToDrop > 0 ? howManyToDrop : 0)
}

Tests

import assert from 'assert'

import { drop } from './drop'

test('with array', () => {
  expect(drop(2)([ 'foo', 'bar', 'baz' ])).toEqual([ 'baz' ])
  expect(drop(3, [ 'foo', 'bar', 'baz' ])).toEqual([])
  expect(drop(4, [ 'foo', 'bar', 'baz' ])).toEqual([])
})

test('with string', () => {
  expect(drop(3, 'rambda')).toEqual('bda')
})

test('with non-positive count', () => {
  expect(drop(0, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
  expect(drop(-1, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
  expect(drop(-Infinity, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
})

test('should return copy', () => {
  const xs = [ 1, 2, 3 ]

  assert.notStrictEqual(drop(0, xs), xs)
  assert.notStrictEqual(drop(-1, xs), xs)
})

Typescript test

import {drop} from 'rambda'

describe('drop', () => {
  it('happy', () => {
    const x = drop(2, 'foo') // $ExpectType string
    x // $ExpectType string
    const xx = drop(2)('foo') // $ExpectType string
    xx // $ExpectType string
    const y = drop(2, [1, 2, 3]) // $ExpectType number[]
    y // $ExpectType number[]
    const yy = drop<number>(2)([1, 2, 3]) // $ExpectType number[]
    yy // $ExpectType number[]
  })
})

dropLast

dropLast<T>(howManyToDrop: number, listOrString: ReadonlyArray<T>): T[]

It returns listOrString with howManyToDrop items dropped from its end.

R.dropLast(2, ['foo', 'bar', 'baz']) // => ['foo']
R.dropLast(2, 'foobar')  // => 'foob'

Try the above R.dropLast example in Rambda REPL

All Typescript definitions

dropLast<T>(howManyToDrop: number, listOrString: ReadonlyArray<T>): T[];
dropLast(howManyToDrop: number, listOrString: string): string;
dropLast<T>(howManyToDrop: number): {
  (listOrString: ReadonlyArray<T>): T[];
  (listOrString: string): string;
};

R.dropLast source

export function dropLast(howManyToDrop, listOrString){
  if (arguments.length === 1){
    return _listOrString => dropLast(howManyToDrop, _listOrString)
  }

  return howManyToDrop > 0 ?
    listOrString.slice(0, -howManyToDrop) :
    listOrString.slice()
}

Tests

import assert from 'assert'

import { dropLast } from './dropLast'

test('with array', () => {
  expect(dropLast(2)([ 'foo', 'bar', 'baz' ])).toEqual([ 'foo' ])
  expect(dropLast(3, [ 'foo', 'bar', 'baz' ])).toEqual([])
  expect(dropLast(4, [ 'foo', 'bar', 'baz' ])).toEqual([])
})

test('with string', () => {
  expect(dropLast(3, 'rambda')).toEqual('ram')
})

test('with non-positive count', () => {
  expect(dropLast(0, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
  expect(dropLast(-1, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
  expect(dropLast(-Infinity, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
})

test('should return copy', () => {
  const xs = [ 1, 2, 3 ]

  assert.notStrictEqual(dropLast(0, xs), xs)
  assert.notStrictEqual(dropLast(-1, xs), xs)
})

5 failed Ramda.dropLast specs

💥 Reason for the failure: ramda method can act as a transducer

var assert = require('assert');

var R = require('../../../../dist/rambda.js');
var eq = require('./shared/eq');
describe('dropLast', function() {
  it('can act as a transducer', function() {
    var dropLast2 = R.dropLast(2);
    assert.deepEqual(R.into([], dropLast2, [1, 3, 5, 7, 9, 1, 2]), [1, 3, 5, 7, 9]);
    assert.deepEqual(R.into([], dropLast2, [1]), []);
  });
});

either

either(firstPredicate: Pred, secondPredicate: Pred): Pred

It returns a new predicate function from firstPredicate and secondPredicate inputs.

This predicate function will return true, if any of the two input predicates return true.

const firstPredicate = x => x > 10
const secondPredicate = x => x % 2 === 0
const predicate = R.either(firstPredicate, secondPredicate)

const result = [
  predicate(15),
  predicate(8),
  predicate(7),
]
//=> [true, true, false]

Try the above R.either example in Rambda REPL

All Typescript definitions

either(firstPredicate: Pred, secondPredicate: Pred): Pred;
either(firstPredicate: Pred): (secondPredicate: Pred) => Pred;

R.either source

export function either(firstPredicate, secondPredicate){
  if (arguments.length === 1){
    return _secondPredicate => either(firstPredicate, _secondPredicate)
  }

  return (...input) =>
    Boolean(firstPredicate(...input) || secondPredicate(...input))
}

Tests

import { either } from './either'

test('with multiple inputs', () => {
  const between = function (
    a, b, c
  ){
    return a < b && b < c
  }
  const total20 = function (
    a, b, c
  ){
    return a + b + c === 20
  }
  const fn = either(between, total20)
  expect(fn(
    7, 8, 5
  )).toBeTrue()
})

test('skip evaluation of the second expression', () => {
  let effect = 'not evaluated'
  const F = function (){
    return true
  }
  const Z = function (){
    effect = 'Z got evaluated'
  }
  either(F, Z)()

  expect(effect).toBe('not evaluated')
})

test('case 1', () => {
  const firstFn = val => val > 0
  const secondFn = val => val * 5 > 10

  expect(either(firstFn, secondFn)(1)).toBeTrue()
})

test('case 2', () => {
  const firstFn = val => val > 0
  const secondFn = val => val === -10
  const fn = either(firstFn)(secondFn)

  expect(fn(-10)).toBeTrue()
})

1 failed Ramda.either specs

💥 Reason for the failure: ramda supports fantasy-land

var S = require('sanctuary');

var R = require('../../../../dist/rambda.js');
var eq = require('./shared/eq');
describe('either', function() {
  it('accepts fantasy-land applicative functors', function() {
    var Just = S.Just;
    var Nothing = S.Nothing;
    eq(R.either(Just(true), Just(true)), Just(true));
    eq(R.either(Just(true), Just(false)), Just(true));
    eq(R.either(Just(false), Just(false)), Just(false));
    eq(R.either(Just(true), Nothing()), Nothing());
    eq(R.either(Nothing(), Just(false)), Nothing());
    eq(R.either(Nothing(), Nothing()), Nothing());
  });
});

endsWith

endsWith(target: string, str: string): boolean

Curried version of String.prototype.endsWith

const str = 'foo-bar'
const target = '-bar'

const result = R.endsWith(target, str)
// => true

Try the above R.endsWith example in Rambda REPL

All Typescript definitions

endsWith(target: string, str: string): boolean;
endsWith(target: string): (str: string) => boolean;

R.endsWith source

export function endsWith(target, str){
  if (arguments.length === 1) return _str => endsWith(target, _str)

  return str.endsWith(target)
}

Tests

import { endsWith } from './endsWith'

test('happy', () => {
  expect(endsWith('bar', 'foo-bar')).toBeTrue()
  expect(endsWith('baz')('foo-bar')).toBeFalse()
})

test('does not work with arrays', () => {
  expect(() => endsWith([ 'c' ], [ 'a', 'b', 'c' ])).toThrow('str.endsWith is not a function')
})

4 failed Ramda.endsWith specs

💥 Reason for the failure: rambda doesn't support arrays

var R = require('../../../../dist/rambda.js');
var eq = require('./shared/eq');

describe('startsWith', function() {
  it('should return true when an array ends with the provided value', function() {
    eq(R.endsWith(['c'], ['a', 'b', 'c']), true);
  });
  it('should return true when an array ends with the provided values', function() {
    eq(R.endsWith(['b', 'c'], ['a', 'b', 'c']), true);
  });
  it('should return false when an array does not end with the provided value', function() {
    eq(R.endsWith(['b'], ['a', 'b', 'c']), false);
  });
  it('should return false when an array does not end with the provided values', function() {
    eq(R.endsWith(['a', 'b'], ['a', 'b', 'c']), false);
  });
});

equals

equals<T>(a: T, b: T): boolean

It deeply compares a and b and returns true if they are equal.

R.equals(
  [1, {a:2}, [{b: 3}]],
  [1, {a:2}, [{b: 3}]]
) // => true

Try the above R.equals example in Rambda REPL

All Typescript definitions

equals<T>(a: T, b: T): boolean;
equals<T>(a: T): (b: T) => boolean;

R.equals source

import { type } from './type'

function parseError(maybeError){
  const typeofError = maybeError.__proto__.toString()
  if (![ 'Error', 'TypeError' ].includes(typeofError)) return []

  return [ typeofError, maybeError.message ]
}

function parseDate(maybeDate){
  if (!maybeDate.toDateString) return [ false ]

  return [ true, maybeDate.getTime() ]
}

function parseRegex(maybeRegex){
  if (maybeRegex.constructor !== RegExp) return [ false ]

  return [ true, maybeRegex.toString() ]
}

export function equals(a, b){
  if (arguments.length === 1) return _b => equals(a, _b)

  const aType = type(a)

  if (aType !== type(b)) return false
  if ([ 'NaN', 'Undefined', 'Null' ].includes(aType)) return true
  if ([ 'Boolean', 'Number', 'String' ].includes(aType))
    return a.toString() === b.toString()

  if (aType === 'Array'){
    const aClone = Array.from(a)
    const bClone = Array.from(b)

    if (aClone.toString() !== bClone.toString()){
      return false
    }

    let loopArrayFlag = true
    aClone.forEach((aCloneInstance, aCloneIndex) => {
      if (loopArrayFlag){
        if (
          aCloneInstance !== bClone[ aCloneIndex ] &&
          !equals(aCloneInstance, bClone[ aCloneIndex ])
        ){
          loopArrayFlag = false
        }
      }
    })

    return loopArrayFlag
  }

  const aRegex = parseRegex(a)
  const bRegex = parseRegex(b)

  if (aRegex[ 0 ]){
    return bRegex[ 0 ] ? aRegex[ 1 ] === bRegex[ 1 ] : false
  } else if (bRegex[ 0 ]) return false

  const aDate = parseDate(a)
  const bDate = parseDate(b)

  if (aDate[ 0 ]){
    return bDate[ 0 ] ? aDate[ 1 ] === bDate[ 1 ] : false
  } else if (bDate[ 0 ]) return false

  const aError = parseError(a)
  const bError = parseError(b)

  if (aError[ 0 ]){
    return bError[ 0 ] ?
      aError[ 0 ] === bError[ 0 ] && aError[ 1 ] === bError[ 1 ] :
      false
  }

  if (aType === 'Object'){
    const aKeys = Object.keys(a)

    if (aKeys.length !== Object.keys(b).length){
      return false
    }

    let loopObjectFlag = true
    aKeys.forEach(aKeyInstance => {
      if (loopObjectFlag){
        const aValue = a[ aKeyInstance ]
        const bValue = b[ aKeyInstance ]

        if (aValue !== bValue && !equals(aValue, bValue)){
          loopObjectFlag = false
        }
      }
    })

    return loopObjectFlag
  }

  return false
}

Tests

import { equals } from './equals'

test('happy', () => {
  const result = equals([ 1, { a : 1 }, [ { b : 3 } ] ], [ 1, { a : 2 }, [ { b : 3 } ] ])

  expect(result).toBeFalse()
})

test('with regex', () => {
  expect(equals(/s/, /s/)).toEqual(true)
  expect(equals(/s/, /d/)).toEqual(false)
  expect(equals(/a/gi, /a/gi)).toEqual(true)
  expect(equals(/a/gim, /a/gim)).toEqual(true)
  expect(equals(/a/gi, /a/i)).toEqual(false)
})

test('not a number', () => {
  expect(equals([ NaN ], [ NaN ])).toBe(true)
})

test('new number', () => {
  expect(equals(new Number(0), new Number(0))).toEqual(true)
  expect(equals(new Number(0), new Number(1))).toEqual(false)
  expect(equals(new Number(1), new Number(0))).toEqual(false)
})

test('new string', () => {
  expect(equals(new String(''), new String(''))).toEqual(true)
  expect(equals(new String(''), new String('x'))).toEqual(false)
  expect(equals(new String('x'), new String(''))).toEqual(false)
  expect(equals(new String('foo'), new String('foo'))).toEqual(true)
  expect(equals(new String('foo'), new String('bar'))).toEqual(false)
  expect(equals(new String('bar'), new String('foo'))).toEqual(false)
})

test('new Boolean', () => {
  expect(equals(new Boolean(true), new Boolean(true))).toEqual(true)
  expect(equals(new Boolean(false), new Boolean(false))).toEqual(true)
  expect(equals(new Boolean(true), new Boolean(false))).toEqual(false)
  expect(equals(new Boolean(false), new Boolean(true))).toEqual(false)
})

test('new Error', () => {
  expect(equals(new Error('XXX'), {})).toEqual(false)
  expect(equals(new Error('XXX'), new TypeError('XXX'))).toEqual(false)
  expect(equals(new Error('XXX'), new Error('YYY'))).toEqual(false)
  expect(equals(new Error('XXX'), new Error('XXX'))).toEqual(true)
  expect(equals(new Error('XXX'), new TypeError('YYY'))).toEqual(false)
})

test('with dates', () => {
  expect(equals(new Date(0), new Date(0))).toEqual(true)
  expect(equals(new Date(1), new Date(1))).toEqual(true)
  expect(equals(new Date(0), new Date(1))).toEqual(false)
  expect(equals(new Date(1), new Date(0))).toEqual(false)
  expect(equals(new Date(0), {})).toEqual(false)
  expect(equals({}, new Date(0))).toEqual(false)
})

test('ramda spec', () => {
  expect(equals({}, {})).toEqual(true)

  expect(equals({
    a : 1,
    b : 2,
  },
  {
    a : 1,
    b : 2,
  })).toEqual(true)

  expect(equals({
    a : 2,
    b : 3,
  },
  {
    b : 3,
    a : 2,
  })).toEqual(true)

  expect(equals({
    a : 2,
    b : 3,
  },
  {
    a : 3,
    b : 3,
  })).toEqual(false)

  expect(equals({
    a : 2,
    b : 3,
    c : 1,
  },
  {
    a : 2,
    b : 3,
  })).toEqual(false)
})

test('works with boolean tuple', () => {
  expect(equals([ true, false ], [ true, false ])).toBeTrue()
  expect(equals([ true, false ], [ true, true ])).toBeFalse()
})

test('works with equal objects within array', () => {
  const objFirst = {
    a : {
      b : 1,
      c : 2,
      d : [ 1 ],
    },
  }
  const objSecond = {
    a : {
      b : 1,
      c : 2,
      d : [ 1 ],
    },
  }

  const x = [ 1, 2, objFirst, null, '', [] ]
  const y = [ 1, 2, objSecond, null, '', [] ]
  expect(equals(x, y)).toBeTrue()
})

test('works with different objects within array', () => {
  const objFirst = { a : { b : 1 } }
  const objSecond = { a : { b : 2 } }

  const x = [ 1, 2, objFirst, null, '', [] ]
  const y = [ 1, 2, objSecond, null, '', [] ]
  expect(equals(x, y)).toBeFalse()
})

test('works with undefined as second argument', () => {
  expect(equals(1, undefined)).toBeFalse()

  expect(equals(undefined, undefined)).toBeTrue()
})

test('various examples', () => {
  expect(equals([ 1, 2, 3 ])([ 1, 2, 3 ])).toBeTrue()

  expect(equals([ 1, 2, 3 ], [ 1, 2 ])).toBeFalse()

  expect(equals(1, 1)).toBeTrue()

  expect(equals(1, '1')).toBeFalse()

  expect(equals({}, {})).toBeTrue()

  expect(equals({
    a : 1,
    b : 2,
  },
  {
    b : 2,
    a : 1,
  })).toBeTrue()

  expect(equals({
    a : 1,
    b : 2,
  },
  {
    a : 1,
    b : 1,
  })).toBeFalse()

  expect(equals({
    a : 1,
    b : false,
  },
  {
    a : 1,
    b : 1,
  })).toBeFalse()

  expect(equals({
    a : 1,
    b : 2,
  },
  {
    b : 2,
    a : 1,
    c : 3,
  })).toBeFalse()

  expect(equals({
    x : {
      a : 1,
      b : 2,
    },
  },
  {
    x : {
      b : 2,
      a : 1,
      c : 3,
    },
  })).toBeFalse()

  expect(equals({
    a : 1,
    b : 2,
  },
  {
    b : 3,
    a : 1,
  })).toBeFalse()

  expect(equals({ a : { b : { c : 1 } } }, { a : { b : { c : 1 } } })).toBeTrue()

  expect(equals({ a : { b : { c : 1 } } }, { a : { b : { c : 2 } } })).toBeFalse()

  expect(equals({ a : {} }, { a : {} })).toBeTrue()

  expect(equals('', '')).toBeTrue()

  expect(equals('foo', 'foo')).toBeTrue()

  expect(equals('foo', 'bar')).toBeFalse()

  expect(equals(0, false)).toBeFalse()

  expect(equals(/\s/g, null)).toBeFalse()

  expect(equals(null, null)).toBeTrue()

  expect(equals(false)(null)).toBeFalse()
})

14 failed Ramda.equals specs

💥 Reason for the failure: rambda doesn't support recursive data structures, objects with same enumerable properties, map/weakmap type of variables | ramda dispatches to equals method recursively

/* global Map, Set, WeakMap, WeakSet */

var R = require('../../../../dist/rambda.js');
var eq = require('./shared/eq');
describe('equals', function() {
  var a = [];
  var b = a;
  it('never considers Boolean primitive equal to Boolean object', function() {
    eq(R.equals(true, new Boolean(true)), false);
    eq(R.equals(new Boolean(true), true), false);
    eq(R.equals(false, new Boolean(false)), false);
    eq(R.equals(new Boolean(false), false), false);
  });
  it('never considers number primitive equal to Number object', function() {
    eq(R.equals(0, new Number(0)), false);
    eq(R.equals(new Number(0), 0), false);
  });
  it('never considers string primitive equal to String object', function() {
    eq(R.equals('', new String('')), false);
    eq(R.equals(new String(''), ''), false);
    eq(R.equals('x', new String('x')), false);
    eq(R.equals(new String('x'), 'x'), false);
  });
  var supportsSticky = false;
  try { RegExp('', 'y'); supportsSticky = true; } catch (e) {}
  var supportsUnicode = false;
  try { RegExp('', 'u'); supportsUnicode = true; } catch (e) {}
  var listA = [1, 2, 3];
  var listB = [1, 3, 2];
  var c = {}; c.v = c;
  var d = {}; d.v = d;
  var e = []; e.push(e);
  var f = []; f.push(f);
  var nestA = {a:[1, 2, {c:1}], b:1};
  var nestB = {a:[1, 2, {c:1}], b:1};
  var nestC = {a:[1, 2, {c:2}], b:1};
  it('handles recursive data structures', function() {
    eq(R.equals(c, d), true);
    eq(R.equals(e, f), true);
    eq(R.equals(nestA, nestB), true);
    eq(R.equals(nestA, nestC), false);
  });
  it('requires that both objects have the same enumerable properties with the same values', function() {
    var a1 = [];
    var a2 = [];
    a2.x = 0;
    var b1 = new Boolean(false);
    var b2 = new Boolean(false);
    b2.x = 0;
    var d1 = new Date(0);
    var d2 = new Date(0);
    d2.x = 0;
    var n1 = new Number(0);
    var n2 = new Number(0);
    n2.x = 0;
    var r1 = /(?:)/;
    var r2 = /(?:)/;
    r2.x = 0;
    var s1 = new String('');
    var s2 = new String('');
    s2.x = 0;
    eq(R.equals(a1, a2), false);
    eq(R.equals(b1, b2), false);
    eq(R.equals(d1, d2), false);
    eq(R.equals(n1, n2), false);
    eq(R.equals(r1, r2), false);
    eq(R.equals(s1, s2), false);
  });
  if (typeof ArrayBuffer !== 'undefined' && typeof Int8Array !== 'undefined') {
    var typArr1 = new ArrayBuffer(10);
    typArr1[0] = 1;
    var typArr2 = new ArrayBuffer(10);
    typArr2[0] = 1;
    var typArr3 = new ArrayBuffer(10);
    var intTypArr = new Int8Array(typArr1);
    typArr3[0] = 0;
    it('handles typed arrays', function() {
      eq(R.equals(typArr1, typArr2), true);
      eq(R.equals(typArr1, typArr3), false);
      eq(R.equals(typArr1, intTypArr), false);
    });
  }
  if (typeof Promise !== 'undefined') {
    it('compares Promise objects by identity', function() {
      var p = Promise.resolve(42);
      var q = Promise.resolve(42);
      eq(R.equals(p, p), true);
      eq(R.equals(p, q), false);
    });
  }
  if (typeof Map !== 'undefined') {
    it('compares Map objects by value', function() {
      eq(R.equals(new Map([]), new Map([])), true);
      eq(R.equals(new Map([]), new Map([[1, 'a']])), false);
      eq(R.equals(new Map([[1, 'a']]), new Map([])), false);
      eq(R.equals(new Map([[1, 'a']]), new Map([[1, 'a']])), true);
      eq(R.equals(new Map([[1, 'a'], [2, 'b']]), new Map([[2, 'b'], [1, 'a']])), true);
      eq(R.equals(new Map([[1, 'a']]), new Map([[2, 'a']])), false);
      eq(R.equals(new Map([[1, 'a']]), new Map([[1, 'b']])), false);
      eq(R.equals(new Map([[1, 'a'], [2, new Map([[3, 'c']])]]), new Map([[1, 'a'], [2, new Map([[3, 'c']])]])), true);
      eq(R.equals(new Map([[1, 'a'], [2, new Map([[3, 'c']])]]), new Map([[1, 'a'], [2, new Map([[3, 'd']])]])), false);
      eq(R.equals(new Map([[[1, 2, 3], [4, 5, 6]]]), new Map([[[1, 2, 3], [4, 5, 6]]])), true);
      eq(R.equals(new Map([[[1, 2, 3], [4, 5, 6]]]), new Map([[[1, 2, 3], [7, 8, 9]]])), false);
    });
    it('dispatches to `equals` method recursively in Set', function() {
      var a = new Map();
      var b = new Map();
      a.set(a, a);
      eq(R.equals(a, b), false);
      a.set(b, b);
      b.set(b, b);
      b.set(a, a);
      eq(R.equals(a, b), true);
    });
  }
  if (typeof Set !== 'undefined') {
    it('compares Set objects by value', function() {
      eq(R.equals(new Set([]), new Set([])), true);
      eq(R.equals(new Set([]), new Set([1])), false);
      eq(R.equals(new Set([1]), new Set([])), false);
      eq(R.equals(new Set([1, 2]), new Set([2, 1])), true);
      eq(R.equals(new Set([1, new Set([2, new Set([3])])]), new Set([1, new Set([2, new Set([3])])])), true);
      eq(R.equals(new Set([1, new Set([2, new Set([3])])]), new Set([1, new Set([2, new Set([4])])])), false);
      eq(R.equals(new Set([[1, 2, 3], [4, 5, 6]]), new Set([[1, 2, 3], [4, 5, 6]])), true);
      eq(R.equals(new Set([[1, 2, 3], [4, 5, 6]]), new Set([[1, 2, 3], [7, 8, 9]])), false);
    });
    it('dispatches to `equals` method recursively in Set', function() {
      var a = new Set();
      var b = new Set();
      a.add(a);
      eq(R.equals(a, b), false);
      a.add(b);
      b.add(b);
      b.add(a);
      eq(R.equals(a, b), true);
    });
  }
  if (typeof WeakMap !== 'undefined') {
    it('compares WeakMap objects by identity', function() {
      var m = new WeakMap([]);
      eq(R.equals(m, m), true);
      eq(R.equals(m, new WeakMap([])), false);
    });
  }
  if (typeof WeakSet !== 'undefined') {
    it('compares WeakSet objects by identity', function() {
      var s = new WeakSet([]);
      eq(R.equals(s, s), true);
      eq(R.equals(s, new WeakSet([])), false);
    });
  }
  it('dispatches to `equals` method recursively', function() {
    function Left(x) { this.value = x; }
    Left.prototype.equals = function(x) {
      return x instanceof Left && R.equals(x.value, this.value);
    };
    function Right(x) { this.value = x; }
    Right.prototype.equals = function(x) {
      return x instanceof Right && R.equals(x.value, this.value);
    };
    eq(R.equals(new Left([42]), new Left([42])), true);
    eq(R.equals(new Left([42]), new Left([43])), false);
    eq(R.equals(new Left(42), {value: 42}), false);
    eq(R.equals({value: 42}, new Left(42)), false);
    eq(R.equals(new Left(42), new Right(42)), false);
    eq(R.equals(new Right(42), new Left(42)), false);
    eq(R.equals([new Left(42)], [new Left(42)]), true);
    eq(R.equals([new Left(42)], [new Right(42)]), false);
    eq(R.equals([new Right(42)], [new Left(42)]), false);
    eq(R.equals([new Right(42)], [new Right(42)]), true);
  });
});

F

F(): boolean

F() // => false

Try the above R.F example in Rambda REPL

All Typescript definitions

F(): boolean;

R.F source

export function F(){
  return false
}

filter

filter<T>(predicate: FilterFunctionArray<T>): (x: T[]) => T[]

It filters list or object input with predicate.

const list = [3, 4, 3, 2]
const listPredicate = (x, index) => x - index > 2

const object = {abc: 'fo', xyz: 'bar', baz: 'foo'}
const objectPredicate = (x, prop) => x.length + prop.length > 5

const result = [
  R.filter(listPredicate, list),
  R.filter(objectPredicate, object)
]
// => [ [3, 4], { xyz: 'bar', baz: 'foo'} ]

Try the above R.filter example in Rambda REPL

All Typescript definitions

filter<T>(predicate: FilterFunctionArray<T>): (x: T[]) => T[];
filter<T>(predicate: FilterFunctionArray<T>, x: T[]): T[];
filter<T, U>(predicate: FilterFunctionObject<T>): (x: Dictionary<T>) => Dictionary<T>;
filter<T>(predicate: FilterFunctionObject<T>, x: Dictionary<T>): Dictionary<T>;

R.filter source

import { _isArray } from './_internals/_isArray'

function filterObject(fn, obj){
  const willReturn = {}

  for (const prop in obj){
    if (fn(
      obj[ prop ], prop, obj
    )){
      willReturn[ prop ] = obj[ prop ]
    }
  }

  return willReturn
}

export function filter(predicate, list){
  if (arguments.length === 1) return _list => filter(predicate, _list)

  if (!list) return []

  if (!_isArray(list)){
    return filterObject(predicate, list)
  }

  let index = 0
  const len = list.length
  const willReturn = []

  while (index < len){
    const value = list[ index ]

    if (predicate(value, index)){
      willReturn.push(value)
    }

    index++
  }

  return willReturn
}

Tests

import Ramda from 'ramda'

import { F } from './F'
import { filter } from './filter'
import { T } from './T'

const sampleObject = {
  a : 1,
  b : 2,
  c : 3,
  d : 4,
}

test('happy', () => {
  const isEven = n => n % 2 === 0

  expect(filter(isEven, [ 1, 2, 3, 4 ])).toEqual([ 2, 4 ])
  expect(filter(isEven, {
    a : 1,
    b : 2,
    d : 3,
  })).toEqual({ b : 2 })
})

test('bad inputs', () => {
  expect(filter(T)(undefined)).toEqual([])
  expect(filter(F, null)).toEqual([])
  expect(() => Ramda.filter(T, null)).toThrow()
  expect(() => Ramda.filter(T, undefined)).toThrow()
})

test('predicate when input is object', () => {
  const obj = {
    a : 1,
    b : 2,
  }
  const predicate = (
    val, prop, inputObject
  ) => {
    expect(inputObject).toEqual(obj)
    expect(typeof prop).toEqual('string')

    return val < 2
  }
  expect(filter(predicate, obj)).toEqual({ a : 1 })
})

test('pass index as second argument', () => {
  let counter = 0
  filter((x, i) => {
    expect(i).toBe(counter)
    counter++
  },
  [ 10, 20, 30 ])
})

test('with object', () => {
  const isEven = n => n % 2 === 0
  const result = filter(isEven, sampleObject)
  const expectedResult = {
    b : 2,
    d : 4,
  }

  expect(result).toEqual(expectedResult)
})

Typescript test

import {filter} from 'rambda'

describe('filter with array', () => {
  it('1 curry', () => {
    const x = filter<number>(a => {
      a // $ExpectType number
      return a > 1
    })([1, 2, 3])
    x // $ExpectType number[]
  })
  it('1', () => {
    const x = filter<number>(
      a => {
        a // $ExpectType number
        return a > 1
      },
      [1, 2, 3]
    )
    x // $ExpectType number[]
  })
  it('2', () => {
    const x = filter<number>(
      (a, b) => {
        a // $ExpectType number
        return a > 1
      },
      [1, 2, 3]
    )
    x // $ExpectType number[]
  })
})

describe('filter with objects', () => {
  it('curry', () => {
    const x = filter<number, number>((a, b, c) => {
      b // $ExpectType string
      c // $ExpectType Dictionary<number>

      return a > 1
    })({a: 1, b: 2})
    x // $ExpectType Dictionary<number>
  })

  it('object with three arguments predicate', () => {
    const x = filter<number>(
      (a, b, c) => {
        b // $ExpectType string
        c // $ExpectType Dictionary<number>

        return a > 1
      },
      {a: 1, b: 2}
    )
    x // $ExpectType Dictionary<number>
  })

  it('object with two arguments predicate', () => {
    const x = filter<number>(
      (a, b) => {
        b // $ExpectType string
        return a > 1
      },
      {a: 1, b: 2}
    )
    x // $ExpectType Dictionary<number>
  })
  it('object with one argument predicate', () => {
    const x = filter<number>(
      a => {
        a // $ExpectType number
        return a > 1
      },
      {a: 1, b: 2}
    )
    x // $ExpectType Dictionary<number>
  })
})

1 failed Ramda.filter specs

💥 Reason for the failure: ramda dispatches to filter method of object

var R = require('../../../../dist/rambda.js');
var eq = require('./shared/eq');
var Maybe = require('./shared/Maybe');

describe('filter', function() {
  var even = function(x) {return x % 2 === 0;};
  it('dispatches to passed-in non-Array object with a `filter` method', function() {
    var f = {filter: function(f) { return f('called f.filter'); }};
    eq(R.filter(function(s) { return s; }, f), 'called f.filter');
  });
  it('correctly uses fantasy-land implementations', function() {
    var m1 = Maybe.Just(-1);
    var m2 = R.filter(function(x) { return x > 0; } , m1);
    eq(m2.isNothing, true);
  });
});

filterAsync

filterAsync<T>(fn: (x: T) => Promise<boolean>, list: T[]): Promise<T[]>

Asynchronous version of R.filter

const predicate = async x => {
  await R.delay(100)
  return x % 2 === 1
}
const result = await R.filterAsync(predicate, [ 1, 2, 3 ])
// => [ 1, 3 ]

Try the above R.filterAsync example in Rambda REPL

All Typescript definitions

filterAsync<T>(fn: (x: T) => Promise<boolean>, list: T[]): Promise<T[]>;
filterAsync<T>(fn: (x: T) => Promise<boolean>, obj: object): Promise<{
  [prop: string]: T
}>;

R.filterAsync source

import { _isArray } from './_internals/_isArray'
import { filter } from './filter'
import { mapAsync } from './mapAsync'

export function filterAsync(predicate, listOrObject){
  if (arguments.length === 1){
    return async holder => filterAsync(predicate, holder)
  }

  return new Promise((resolve, reject) => {
    mapAsync(predicate, listOrObject)
      .then(predicateResult => {
        if (_isArray(predicateResult)){
          const filtered = listOrObject.filter((_, i) => predicateResult[ i ])

          return resolve(filtered)
        }
        const filtered = filter((_, prop) => predicateResult[ prop ],
          listOrObject)

        return resolve(filtered)
      })
      .catch(reject)
  })
}

Tests

import { delay } from './delay'
import { filterAsync } from './filterAsync'

test('happy', async () => {
  const predicate = async x => {
    await delay(100)

    return x % 2 === 1
  }
  const result = await filterAsync(predicate, [ 1, 2, 3 ])
  expect(result).toEqual([ 1, 3 ])
})

test('with object', async () => {
  const predicate = async (x, prop) => {
    expect(typeof prop).toBe('string')
    await delay(100)

    return x % 2 === 1
  }
  const result = await filterAsync(predicate, {
    a : 1,
    b : 2,
    c : 3,
    d : 4,
    e : 5,
  })

  expect(result).toEqual({
    a : 1,
    c : 3,
    e : 5,
  })
})

find

find<T>(predicate: (a: T) => boolean, arr: ReadonlyArray<T>): T | undefined

It returns the first element of list that satisfy the predicate.

If there is no such element, it returns undefined.

const predicate = x => R.type(x.foo) === 'Number'
const list = [{foo: 'bar'}, {foo: 1}]

const result = R.find(predicate, list)
// => {foo: 1}

Try the above R.find example in Rambda REPL

All Typescript definitions

find<T>(predicate: (a: T) => boolean, arr: ReadonlyArray<T>): T | undefined;
find<T>(predicate: (a: T) => boolean): (arr: ReadonlyArray<T>) => T | undefined;

R.find source

export function find(predicate, list){
  if (arguments.length === 1) return _list => find(predicate, _list)
  let index = 0
  const len = list.length

  while (index < len){
    const value = list[ index ]
    if (predicate(value, index)){
      return value
    }

    index++
  }
}

Tests

import { find } from './find'
import { propEq } from './propEq'

const list = [ { a : 1 }, { a : 2 }, { a : 3 } ]

test('happy', () => {
  const fn = propEq('a', 2)
  expect(find(fn, list)).toEqual({ a : 2 })
})

test('with curry', () => {
  const fn = propEq('a', 4)
  expect(find(fn)(list)).toBeUndefined()
})

test('with empty list', () => {
  expect(find(() => true, [])).toBeUndefined()
})

findIndex

findIndex<T>(findFn: (a: T) => boolean, arr: ReadonlyArray<T>): number

It returns the index of the first element of list satisfying the predicate function.

If there is no such element, then -1 is returned.

const predicate = x => R.type(x.foo) === 'Number'
const list = [{foo: 'bar'}, {foo: 1}]

const result = R.findIndex(predicate, list)
// => 1

Try the above R.findIndex example in Rambda REPL

All Typescript definitions

findIndex<T>(findFn: (a: T) => boolean, arr: ReadonlyArray<T>): number;
findIndex<T>(findFn: (a: T) => boolean): (arr: ReadonlyArray<T>) => number;

R.findIndex source

export function findIndex(predicate, list){
  if (arguments.length === 1) return _list => findIndex(predicate, _list)

  const len = list.length
  let index = -1

  while (++index < len){
    if (predicate(list[ index ], index)){
      return index
    }
  }

  return -1
}

Tests

import { findIndex } from './findIndex'
import { propEq } from './propEq'

test('happy', () => {
  expect(findIndex(propEq('a', 2))([ { a : 1 }, { a : 2 }, { a : 3 } ])).toEqual(1)

  expect(findIndex(propEq('a', 1))([ { a : 1 }, { a : 2 }, { a : 3 } ])).toEqual(0)

  expect(findIndex(propEq('a', 4))([ { a : 1 }, { a : 2 }, { a : 3 } ])).toEqual(-1)
})

test('pass index as second argument', () => {
  findIndex((x, i) => {
    expect(typeof x).toBe('number')
    expect(typeof i).toBe('number')
  })([ 10, 12, 15 ])
})

findLast

findLast<T>(fn: (a: T) => boolean, list: T[]): T | undefined

It returns the last element of list satisfying the predicate function.

If there is no such element, then undefined is returned.

const predicate = x => R.type(x.foo) === 'Number'
const list = [{foo: 0}, {foo: 1}]

const result = R.findLast(predicate, list)
// => {foo: 1}

Try the above R.findLast example in Rambda REPL

All Typescript definitions

findLast<T>(fn: (a: T) => boolean, list: T[]): T | undefined;
findLast<T>(fn: (a: T) => boolean): (list: T[]) => T | undefined;

R.findLast source

export function findLast(predicate, list){
  if (arguments.length === 1) return _list => findLast(predicate, _list)

  let index = list.length

  while (--index >= 0){
    if (predicate(list[ index ], index)){
      return list[ index ]
    }
  }

  return undefined
}

Tests

import { findLast } from './findLast'

test('happy', () => {
  const result = findLast((x, i) => {
    expect(typeof i).toBe('number')

    return x > 1
  },
  [ 1, 1, 1, 2, 3, 4, 1 ])
  expect(result).toEqual(4)

  expect(findLast(x => x === 0, [ 0, 1, 1, 2, 3, 4, 1 ])).toEqual(0)
})

test('with curry', () => {
  expect(findLast(x => x > 1)([ 1, 1, 1, 2, 3, 4, 1 ])).toEqual(4)
})

const obj1 = { x : 100 }
const obj2 = { x : 200 }
const a = [ 11, 10, 9, 'cow', obj1, 8, 7, 100, 200, 300, obj2, 4, 3, 2, 1, 0 ]
const even = function (x){
  return x % 2 === 0
}
const gt100 = function (x){
  return x > 100
}
const isStr = function (x){
  return typeof x === 'string'
}
const xGt100 = function (o){
  return o && o.x > 100
}

test('ramda 1', () => {
  expect(findLast(even, a)).toEqual(0)
  expect(findLast(gt100, a)).toEqual(300)
  expect(findLast(isStr, a)).toEqual('cow')
  expect(findLast(xGt100, a)).toEqual(obj2)
})

test('ramda 2', () => {
  expect(findLast(even, [ 'zing' ])).toEqual(undefined)
})

test('ramda 3', () => {
  expect(findLast(even, [ 2, 3, 5 ])).toEqual(2)
})

test('ramda 4', () => {
  expect(findLast(even, [])).toEqual(undefined)
})

findLastIndex

findLastIndex<T>(fn: (a: T) => boolean, list: T[]): number

It returns the index of the last element of list satisfying the predicate function.

If there is no such element, then -1 is returned.

const predicate = x => R.type(x.foo) === 'Number'
const list = [{foo: 0}, {foo: 1}]

const result = R.findLastIndex(predicate, list)
// => 1

Try the above R.findLastIndex example in Rambda REPL

All Typescript definitions

findLastIndex<T>(fn: (a: T) => boolean, list: T[]): number;
findLastIndex<T>(fn: (a: T) => boolean): (list: T[]) => number;

R.findLastIndex source

export function findLastIndex(fn, list){
  if (arguments.length === 1) return _list => findLastIndex(fn, _list)

  let index = list.length

  while (--index >= 0){
    if (fn(list[ index ], index)){
      return index
    }
  }

  return -1
}

Tests

import { findLastIndex } from './findLastIndex'

test('happy', () => {
  const result = findLastIndex((x, i) => {
    expect(typeof i).toBe('number')

    return x > 1
  },
  [ 1, 1, 1, 2, 3, 4, 1 ])

  expect(result).toEqual(5)

  expect(findLastIndex(x => x === 0, [ 0, 1, 1, 2, 3, 4, 1 ])).toEqual(0)
})

test('with curry', () => {
  expect(findLastIndex(x => x > 1)([ 1, 1, 1, 2, 3, 4, 1 ])).toEqual(5)
})

const obj1 = { x : 100 }
const obj2 = { x : 200 }
const a = [ 11, 10, 9, 'cow', obj1, 8, 7, 100, 200, 300, obj2, 4, 3, 2, 1, 0 ]
const even = function (x){
  return x % 2 === 0
}
const gt100 = function (x){
  return x > 100
}
const isStr = function (x){
  return typeof x === 'string'
}
const xGt100 = function (o){
  return o && o.x > 100
}

test('ramda 1', () => {
  expect(findLastIndex(even, a)).toEqual(15)
  expect(findLastIndex(gt100, a)).toEqual(9)
  expect(findLastIndex(isStr, a)).toEqual(3)
  expect(findLastIndex(xGt100, a)).toEqual(10)
})

test('ramda 2', () => {
  expect(findLastIndex(even, [ 'zing' ])).toEqual(-1)
})

test('ramda 3', () => {
  expect(findLastIndex(even, [ 2, 3, 5 ])).toEqual(0)
})

test('ramda 4', () => {
  expect(findLastIndex(even, [])).toEqual(-1)
})

flatten

flatten<T>(x: ReadonlyArray<T> | ReadonlyArray<T[]> | ReadonlyArray<ReadonlyArray<T>>): T[]

It deeply flattens an array.

const result = R.flatten([
  1, 
  2, 
  [3, 30, [300]], 
  [4]
])
// => [ 1, 2, 3, 30, 300, 4 ]

Try the above R.flatten example in Rambda REPL

All Typescript definitions

flatten<T>(x: ReadonlyArray<T> | ReadonlyArray<T[]> | ReadonlyArray<ReadonlyArray<T>>): T[];

R.flatten source

import { _isArray } from './_internals/_isArray'

export function flatten(list, input){
  const willReturn = input === undefined ? [] : input

  for (let i = 0; i < list.length; i++){
    if (_isArray(list[ i ])){
      flatten(list[ i ], willReturn)
    } else {
      willReturn.push(list[ i ])
    }
  }

  return willReturn
}

Tests

import { flatten } from './flatten'

test('happy', () => {
  expect(flatten([ 1, 2, 3, [ [ [ [ [ 4 ] ] ] ] ] ])).toEqual([ 1, 2, 3, 4 ])

  expect(flatten([ 1, [ 2, [ [ 3 ] ] ], [ 4 ] ])).toEqual([ 1, 2, 3, 4 ])

  expect(flatten([ 1, [ 2, [ [ [ 3 ] ] ] ], [ 4 ] ])).toEqual([ 1, 2, 3, 4 ])

  expect(flatten([ 1, 2, [ 3, 4 ], 5, [ 6, [ 7, 8, [ 9, [ 10, 11 ], 12 ] ] ] ])).toEqual([ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 ])
})

test('readme example', () => {
  const result = flatten([ 1, 2, [ 3, 30, [ 300 ] ], [ 4 ] ])
  expect(result).toEqual([ 1, 2, 3, 30, 300, 4 ])
})

flip

flip<T, U, TResult>(fn: (arg0: T, arg1: U) => TResult): (arg1: U, arg0?: T) => TResult

It returns function which calls fn with exchanged first and second argument.

const subtractFlip = R.flip(R.subtract)

const result = [
  subtractFlip(1,7),
  R.flip(1,6)
]  
// => [6, -6]

Try the above R.flip example in Rambda REPL

All Typescript definitions

flip<T, U, TResult>(fn: (arg0: T, arg1: U) => TResult): (arg1: U, arg0?: T) => TResult;
flip<F extends (...args: any) => any, P extends FunctionToolbelt.Parameters<F>>(fn: F): FunctionToolbelt.Curry<(...args: ListToolbelt.Merge<[P[1], P[0]], P>) => FunctionToolbelt.Return<F>>;

R.flip source

import { curryN } from './curryN'

function flipExport(fn){
  const flipedFn = (...input) => {
    const missing = fn.length - input.length

    if (missing <= 0) return fn(
      input[ 1 ], input[ 0 ], ...input.slice(2)
    )

    if (input.length === 0) return flipedFn

    if (input.length === 1)
      return curryN(missing, (...rest) => {
        const args = [ rest[ 0 ], input[ 0 ], ...rest.slice(1) ]

        return fn(...args)
      })

    // input.length >= 2
    return curryN(missing, (...rest) => {
      const args = [ input[ 1 ], input[ 0 ], ...input.slice(2), ...rest ]

      return fn(...args)
    })
  }

  return flipedFn
}

export function flip(fn){
  return flipExport(fn)
}

Tests

import { flip } from './flip'
import { subtract } from './subtract'
import { update } from './update'

test('function with arity of 2', () => {
  const subtractFlipped = flip(subtract)

  expect(subtractFlipped(1)(7)).toEqual(6)
  expect(subtractFlipped(1, 7)).toEqual(6)
  expect(subtractFlipped(
    1, 7, 9
  )).toEqual(6)
})

test('function with arity of 3', () => {
  const updateFlipped = flip(update)

  const result = updateFlipped(
    8, 0, [ 1, 2, 3 ]
  )
  const curriedResult = updateFlipped(8, 0)([ 1, 2, 3 ])
  const tripleCurriedResult = updateFlipped(8)(0)([ 1, 2, 3 ])

  expect(result).toEqual([ 8, 2, 3 ])
  expect(curriedResult).toEqual([ 8, 2, 3 ])
  expect(tripleCurriedResult).toEqual([ 8, 2, 3 ])
})

test('function with arity of 4', () => {
  const testFunction = (
    a, b, c, d
  ) => `${ a },${ b },${ c },${ d }`

  const flippedFn = flip(testFunction)

  const result1 = flippedFn(2)(1)(3)(4)
  const result2 = flippedFn(2)(
    1, 3, 4
  )
  const result3 = flippedFn(2, 1)(3, 4)
  const result4 = flippedFn(
    2, 1, 3
  )(4)
  const result5 = flippedFn(
    2, 1, 3, 4
  )

  const expected = '1,2,3,4'

  expect(result1).toEqual(expected)
  expect(result2).toEqual(expected)
  expect(result3).toEqual(expected)
  expect(result4).toEqual(expected)
  expect(result5).toEqual(expected)
})

Typescript test

import * as R from 'ramda'
import {flip, subtract} from 'rambda'

describe('R.flip', () => {
  it('function with arity of 2', () => {
    const subtractFlipped = flip(subtract)
    const result = subtractFlipped(1, 7)
    const curriedResult = subtractFlipped(1)(7)
    curriedResult // $ExpectType number

    // This is wrong
    // ============================================
    result // $ExpectType (y: number) => number
  })

  it('function with arity of 3', () => {
    function testFunction(a: number, b: string, c: number): string {
      return `${b}==${a + c}`
    }
    const flippedTestFunction = flip(testFunction)

    const result = flippedTestFunction('foo', 1, 2)
    result // $ExpectType string
  })
})

describe('Ramda.flip', () => {
  it('function with arity of 2', () => {
    const subtractFlipped = R.flip(R.subtract)
    const result = subtractFlipped(1, 7)
    const curriedResult = subtractFlipped(1)(7)
    curriedResult // $ExpectType number

    // This is wrong
    // ============================================
    result // $ExpectType (b: number) => number
  })
})

4 failed Ramda.flip specs

💥 Reason for the failure: rambda flip work only for functions with two arguments

var jsv = require('jsverify');

var R = require('../../../../dist/rambda.js');
var eq = require('./shared/eq');
var funcN = require('./shared/funcN');
describe('flip', function() {
  it('returns a function which inverts the first two arguments to the supplied function', function() {
    var f = function(a, b, c) {return a + ' ' + b + ' ' + c;};
    var g = R.flip(f);
    eq(f('a', 'b', 'c'), 'a b c');
    eq(g('a', 'b', 'c'), 'b a c');
  });
  it('returns a curried function', function() {
    var f = function(a, b, c) {return a + ' ' + b + ' ' + c;};
    var g = R.flip(f)('a');
    eq(g('b', 'c'), 'b a c');
  });
  it('returns a function with the correct arity', function() {
    var f2 = function(a, b) {return a + ' ' + b;};
    var f3 = function(a, b, c) {return a + ' ' + b + ' ' + c;};
    eq(R.flip(f2).length, 2);
    eq(R.flip(f3).length, 3);
  });
});
describe('flip properties', function() {
  jsv.property('inverts first two arguments', funcN(3), jsv.json, jsv.json, jsv.json, function(f, a, b, c) {
    var g = R.flip(f);
    return R.equals(f(a, b, c), g(b, a, c));
  });
});

forEach

forEach<T>(fn: (x: T) => void, list: T[]): T[]

It applies iterable function over all members of list and returns list.

const sideEffect = {}
const result = R.forEach(
  x => sideEffect[`foo${x}`] = x
)([1, 2])

sideEffect //=> {foo1: 1, foo2: 2}
result //=> [1, 2]

Try the above R.forEach example in Rambda REPL

All Typescript definitions

forEach<T>(fn: (x: T) => void, list: T[]): T[];
forEach<T>(fn: (x: T) => void): (list: T[]) => T[];
forEach<T>(fn: (x: T) => void, list: ReadonlyArray<T>): ReadonlyArray<T>;
forEach<T>(fn: (x: T) => void): (list: ReadonlyArray<T>) => ReadonlyArray<T>;
forEach<T>(fn: (value: T, key: string, obj: { [key: string]: T }) => void, obj: { [key: string]: T }): void;
forEach<T>(fn: (value: T, key: string, obj: { [key: string]: T }) => void): (obj: { [key: string]: T }) => void;

R.forEach source

import {_isArray} from './_internals/_isArray'
import {_keys} from './_internals/_keys'

export function forEach(fn, list){
  if (arguments.length === 1) return _list => forEach(fn, _list)

  if (list === undefined){
    return
  }

  if (_isArray(list)) {
    let index = 0
    const len = list.length

    while (index < len){
      fn(list[ index ], index, list)
      index++
    }
  } else {
    let index = 0
    const keys = _keys(list)
    const len = keys.length

    while (index < len){
      const key = keys[ index ]
      fn(list[ key ], key, list)
      index++
    }
  }

  return list
}

Tests

import { forEach } from './forEach'
import { type } from './type'

test('iterate over object', () => {
  const obj = {
    a : 1,
    b : [ 1, 2 ],
    c : { d : 7 },
    f : 'foo',
  }
  const result = {}
  const returned = forEach((
    val, prop, inputObj
  ) => {
    expect(type(inputObj)).toBe('Object')
    result[ prop ] = `${ prop }-${ type(val) }`
  })(obj)

  const expected = {
    a : 'a-Number',
    b : 'b-Array',
    c : 'c-Object',
    f : 'f-String',
  }

  expect(result).toEqual(expected)
  expect(returned).toEqual(obj)
})

test('happy', () => {
  const sideEffect = {}
  forEach(x => sideEffect[ `foo${ x }` ] = x + 10)([ 1, 2 ])

  expect(sideEffect).toEqual({
    foo1 : 11,
    foo2 : 12,
  })
})

test('happy 2', () => {
  const list = [
    {
      x : 1,
      y : 2,
    },
    {
      x : 100,
      y : 200,
    },
    {
      x : 300,
      y : 400,
    },
    {
      x : 234,
      y : 345,
    },
  ]
  const sideEffect = {}
  const result = forEach(elem => {
    sideEffect[ elem.x ] = elem.y
  }, list)
  const expectedSideEffect = {
    1   : 2,
    100 : 200,
    300 : 400,
    234 : 345,
  }

  expect(sideEffect).toEqual(expectedSideEffect)
  expect(result).toEqual(list)
})

test('with empty list', () => {
  const list = []
  const result = forEach(x => x * x)(list)

  expect(result).toEqual(list)
})

test('returns the input', () => {
  const list = [ 1, 2, 3 ]
  const result = forEach(x => x * x)(list)

  expect(result).toEqual(list)
})

test('pass index as second argument', () => {
  const list = [ 11, 21, 31 ]
  const indexes = []
  const result = forEach((x, i) => indexes.push(i))(list)

  expect(indexes).toEqual([ 0, 1, 2 ])
})

1 failed Ramda.forEach specs

💥 Reason for the failure: ramda method dispatches to forEach method

var R = require('../../../../dist/rambda.js');
var eq = require('./shared/eq');

describe('forEach', function() {
  var list = [{x: 1, y: 2}, {x: 100, y: 200}, {x: 300, y: 400}, {x: 234, y: 345}];
  it('dispatches to `forEach` method', function() {
    var dispatched = false;
    var fn = function() {};
    function DummyList() {}
    DummyList.prototype.forEach = function(callback) {
      dispatched = true;
      eq(callback, fn);
    };
    R.forEach(fn, new DummyList());
    eq(dispatched, true);
  });
});

fromPairs

fromPairs<V>(listOfPairs: KeyValuePair<string, V>[]): { [index: string]: V }

It transforms a listOfPairs to an object.

const listOfPairs = [ [ 'a', 1 ], [ 'b', 2 ], [ 'c', [ 3, 4 ] ] ]
const expected = {
  a : 1,
  b : 2,
  c : [ 3, 4 ],
}

const result = R.fromPairs(listOfPairs)
// => `result` is equal to `expected`

Try the above R.fromPairs example in Rambda REPL

All Typescript definitions

fromPairs<V>(listOfPairs: KeyValuePair<string, V>[]): { [index: string]: V };
fromPairs<V>(listOfPairs: KeyValuePair<number, V>[]): { [index: number]: V };

R.fromPairs source

export function fromPairs(listOfPairs){
  const toReturn = {}
  listOfPairs.forEach(([ prop, value ]) => toReturn[ prop ] = value)

  return toReturn
}

Tests

import { fromPairs } from './fromPairs'

const list = [
  [ 'a', 1 ],
  [ 'b', 2 ],
  [ 'c', [ 3, 4 ] ],
]
const expected = {
  a : 1,
  b : 2,
  c : [ 3, 4 ],
}

test('happy', () => {
  expect(fromPairs(list)).toEqual(expected)
})

getter

getter<T>(keyOrKeys: string | string[] | undefined): T

The set of methods R.setter, R.getter and R.reset allow different parts of your logic to access comminicate indirectly via shared cache object.

Usually these methods show that you might need to refactor to classes. Still, they can be helpful meanwhile.

R.getter: It provides access to the cache object. If undefined is used as a key, this method will return the whole cache object. If string is passed, then it will return cache value for this key. If array of string is passed, then it assume that this is array of keys and it will return the corresponding cache values for these keys.

R.setter: It allows cache object's keys to be changed. You can either set individual key-value pairs with R.setter(key, value) or you pass directly object, which will be merged with the cache object.

R.reset: It resets the cache object.

R.setter('foo','bar')
R.setter('a', 1)
R.getter(['foo','a']) // => {foo: 'bar', a: 1}

R.setter('a', 2)
R.getter('a') // => 2
R.reset()
R.getter('a') // => undefined

Try the above R.getter example in Rambda REPL

All Typescript definitions

getter<T>(keyOrKeys: string | string[] | undefined): T;

R.getter source

import { merge } from './merge'
import { pick } from './pick'
import { type } from './type'

let holder = {}

/**
 * Pass string to get value
 * Pass array to get object of values
 * Pass undefined to get all data
 */
export function getter(key){
  const typeKey = type(key)

  if (typeKey === 'String') return holder[ key ]

  if (typeKey === 'Array') return pick(key, holder)

  return holder
}

export function setter(maybeKey, maybeValue){
  const typeKey = type(maybeKey)
  const typeValue = type(maybeValue)

  if (typeKey === 'String'){
    if (typeValue === 'Function'){
      return holder[ maybeKey ] = maybeValue(holder[ maybeKey ])
    }

    return holder[ maybeKey ] = maybeValue
  }

  if (typeKey !== 'Object') return

  holder = merge(holder, maybeKey)
}

export function reset(){
  holder = {}
}

Tests

import { add } from './add'
import { getter, reset, setter } from './getter'

afterEach(() => {
  reset()
})

test('happy', () => {
  const key = 'foo'
  setter(key, 1)

  expect(getter(key)).toBe(1)
})

test('docs example', () => {
  setter('foo', 'bar')
  setter('a', 1)
  expect(getter([ 'foo', 'a' ])).toEqual({
    foo : 'bar',
    a   : 1,
  })

  setter('a', 2)
  expect(getter('a')).toBe(2)
  reset()
  expect(getter('a')).toBeUndefined()
})

test('when array is key in getter', () => {
  setter({
    a : 1,
    b : 2,
    c : 3,
  })

  expect(getter([ 'a', 'b' ])).toEqual({
    a : 1,
    b : 2,
  })
})

test('getter with undefined as key returns all', () => {
  const data = {
    a : 1,
    b : 2,
    c : 3,
  }

  setter(data)

  expect(getter()).toEqual(data)
})

test('function as setter value', () => {
  const data = {
    a : 1,
    b : 2,
    c : 3,
  }

  setter(data)
  setter('a', add(10))

  expect(getter()).toEqual({
    a : 11,
    b : 2,
    c : 3,
  })
})

test('setter fallbacks to undefined', () => {
  expect(setter()).toBeUndefined
})

glue

glue(input: string, glueString?: string): string

It transforms multiline string to single line by gluing together the separate lines with the glueString and removing the empty spaces. By default glueString is equal to single space, so if that is what you need, then you can just pass a single argument.

const result = R.glue(`
  foo
  bar
  baz
`)
// => 'foo bar baz'

Try the above R.glue example in Rambda REPL

All Typescript definitions

glue(input: string, glueString?: string): string;

R.glue source

export function glue(input, glueChar){
  return input
    .split('\n')
    .filter(x => x.trim().length > 0)
    .map(x => x.trim())
    .join(glueChar === undefined ? ' ' : glueChar)
}

Tests

import { glue } from './glue'

test('empty string as a glue', () => {
  const result = glue(`
    foo
    bar
    baz
  `,
  '')

  const expectedResult = 'foobarbaz'

  expect(result).toBe(expectedResult)
})

test('case 0', () => {
  const zero = 'node node_modules/jest'
  const first = '--runInBand'
  const last = '-- src/a.spec.js'
  const flag = false
  const result = glue(`
    ${ zero }
    ${ first }
    ${ flag ? '--env=node' : '' }
    ${ last }
  `)

  const expectedResult = `${ zero } ${ first } ${ last }`

  expect(result).toBe(expectedResult)
})

test('case 1', () => {
  const zero = 'node node_modules/jest'
  const first = '--runInBand'
  const last = '-- src/a.spec.js'
  const flag = true
  const result = glue(`
    ${ zero }
    ${ first }
    ${ flag ? '--env=node' : '' }
    ${ last }
  `)

  const expectedResult = `${ zero } ${ first } --env=node ${ last }`

  expect(result).toBe(expectedResult)
})

test('case 2', () => {
  const first = '--runInBand'
  const result = glue(`
    zero
    ${ first }
    last
  `)
  const expectedResult = `zero ${ first } last`

  expect(result).toBe(expectedResult)
})

test('case 3', () => {
  const result = glue(`
    foo
    bar
    baz
  `)

  const expectedResult = 'foo bar baz'

  expect(result).toBe(expectedResult)
})

test('with glue', () => {
  const result = glue(`
    foo
    bar
    baz
  `,
  '==')

  const expectedResult = 'foo==bar==baz'

  expect(result).toBe(expectedResult)
})

groupBy

groupBy<T>(groupFn: (a: T) => string, list: ReadonlyArray<T>): { [index: string]: T[] }

It splits list according to a provided groupFn function and returns an object.

const list = [ 'a', 'b', 'aa', 'bb' ]
const groupFn = x => x.length

const result = R.groupBy(groupFn, list)
// => { '1': ['a', 'b'], '2': ['aa', 'bb'] }

Try the above R.groupBy example in Rambda REPL

All Typescript definitions

groupBy<T>(groupFn: (a: T) => string, list: ReadonlyArray<T>): { [index: string]: T[] };
groupBy<T>(groupFn: (a: T) => string): (list: ReadonlyArray<T>) => { [index: string]: T[] };

R.groupBy source

export function groupBy(groupFn, list){
  if (arguments.length === 1) return _list => groupBy(groupFn, _list)

  const result = {}
  for (let i = 0; i < list.length; i++){
    const item = list[ i ]
    const key = groupFn(item)

    if (!result[ key ]){
      result[ key ] = []
    }

    result[ key ].push(item)
  }

  return result
}

Tests

import { groupBy } from './groupBy'
import { prop } from './prop'

test('groupBy', () => {
  const list = [
    {
      age  : 12,
      name : 'john',
    },
    {
      age  : 12,
      name : 'jack',
    },
    {
      age  : 24,
      name : 'mary',
    },
    {
      age  : 24,
      name : 'steve',
    },
  ]
  const expectedResult = {
    12 : [
      {
        age  : 12,
        name : 'john',
      },
      {
        age  : 12,
        name : 'jack',
      },
    ],
    24 : [
      {
        age  : 24,
        name : 'mary',
      },
      {
        age  : 24,
        name : 'steve',
      },
    ],
  }

  expect(groupBy(prop('age'))(list)).toEqual(expectedResult)
  expect(groupBy(prop('age'), list)).toEqual(expectedResult)
})

1 failed Ramda.groupBy specs

💥 Reason for the failure: ramda support transforms

var R = require('../../../../dist/rambda.js');
var eq = require('./shared/eq');
var _isTransformer = require('rambda/internal/_isTransformer');

describe('groupBy', function() {
  it('dispatches on transformer objects in list position', function() {
    var byType = R.prop('type');
    var xf = {
      '@@transducer/init': function() { return {}; },
      '@@transducer/result': function(x) { return x; },
      '@@transducer/step': R.mergeRight
    };
    eq(_isTransformer(R.groupBy(byType, xf)), true);
  });
});

groupWith

groupWith<T>(compareFn: (x: T, y: T) => boolean): (list: ReadonlyArray<T>) => T[][]

It returns separated version of list, where separation is done with equality compareFn function.

const compareFn = (x, y) => x === y
const list = [1, 2, 2, 1, 1, 2]

const result = R.groupWith(isConsecutive, list)
// => [[1], [2,2], [1,1], [2]]

Try the above R.groupWith example in Rambda REPL

All Typescript definitions

groupWith<T>(compareFn: (x: T, y: T) => boolean): (list: ReadonlyArray<T>) => T[][];
groupWith<T>(compareFn: (x: T, y: T) => boolean, list: ReadonlyArray<T>): T[][];
groupWith<T>(compareFn: (x: T, y: T) => boolean, list: string): string[];

R.groupWith source

import { _isArray } from './_internals/_isArray'

export function groupWith(compareFn, list){
  if (!_isArray(list)) throw new TypeError('list.reduce is not a function')

  const clone = list.slice()

  if (list.length === 1) return [ clone ]

  const toReturn = []
  let holder = []

  clone.reduce((
    prev, current, i
  ) => {
    if (i === 0) return current

    const okCompare = compareFn(prev, current)
    const holderIsEmpty = holder.length === 0
    const lastCall = i === list.length - 1

    if (okCompare){
      if (holderIsEmpty) holder.push(prev)
      holder.push(current)
      if (lastCall) toReturn.push(holder)

      return current
    }

    if (holderIsEmpty){
      toReturn.push([ prev ])
      if (lastCall) toReturn.push([ current ])

      return current
    }

    toReturn.push(holder)
    if (lastCall) toReturn.push([ current ])
    holder = []

    return current
  }, undefined)

  return toReturn
}

Tests

import { equals } from './equals'
import { groupWith } from './groupWith'

test('issue is fixed', () => {
  const result = groupWith(equals, [ 1, 2, 2, 3 ])
  const expected = [ [ 1 ], [ 2, 2 ], [ 3 ] ]
  expect(result).toEqual(expected)
})

test('long list', () => {
  const result = groupWith(equals, [
    0,
    1,
    1,
    2,
    3,
    5,
    8,
    13,
    21,
    21,
    21,
    1,
    2,
  ])

  const expected = [
    [ 0 ],
    [ 1, 1 ],
    [ 2 ],
    [ 3 ],
    [ 5 ],
    [ 8 ],
    [ 13 ],
    [ 21, 21, 21 ],
    [ 1 ],
    [ 2 ],
  ]
  expect(result).toEqual(expected)
})

test('readme example', () => {
  const list = [ 4, 3, 6, 2, 2, 1 ]

  const result = groupWith((a, b) => a - b === 1, list)
  const expected = [ [ 4, 3 ], [ 6 ], [ 2 ], [ 2, 1 ] ]
  expect(result).toEqual(expected)
})

test('throw with string as input', () => {
  expect(() => groupWith(equals, 'Mississippi')).toThrowWithMessage(TypeError,
    'list.reduce is not a function')
})

const isConsecutive = function (a, b){
  return a + 1 === b
}

test('fix coverage', () => {
  expect(groupWith(isConsecutive, [ 1, 2, 3, 0 ])).toEqual([ [ 1, 2, 3 ], [ 0 ] ])
})

test('from ramda 0', () => {
  expect(groupWith(equals, [])).toEqual([])
  expect(groupWith(isConsecutive, [])).toEqual([])
})

test('from ramda 1', () => {
  expect(groupWith(isConsecutive, [ 4, 3, 2, 1 ])).toEqual([
    [ 4 ],
    [ 3 ],
    [ 2 ],
    [ 1 ],
  ])
})

test('from ramda 2', () => {
  expect(groupWith(isConsecutive, [ 1, 2, 3, 4 ])).toEqual([ [ 1, 2, 3, 4 ] ])
})

test('from ramda 3', () => {
  expect(groupWith(isConsecutive, [ 1, 2, 2, 3 ])).toEqual([
    [ 1, 2 ],
    [ 2, 3 ],
  ])
  expect(groupWith(isConsecutive, [ 1, 2, 9, 3, 4 ])).toEqual([
    [ 1, 2 ],
    [ 9 ],
    [ 3, 4 ],
  ])
})

test('list with single item', () => {
  const result = groupWith(equals, [ 0 ])

  const expected = [ [ 0 ] ]
  expect(result).toEqual(expected)
})

2 failed Ramda.groupWith specs

💥 Reason for the failure: ramda support string

var R = require('../../../../dist/rambda.js');
var eq = require('./shared/eq');

describe('groupWith', function() {
  it('can be turned into the original list through concatenation', function() {
    var list = [1, 1, 2, 3, 4, 4, 5, 5];
    eq(R.unnest(R.groupWith(R.equals, list)), list);
    eq(R.unnest(R.groupWith(R.complement(R.equals), list)), list);
    eq(R.unnest(R.groupWith(R.T, list)), list);
    eq(R.unnest(R.groupWith(R.F, list)), list);
  });
  it('also works on strings', function() {
    eq(R.groupWith(R.equals)('Mississippi'), ['M','i','ss','i','ss','i','pp','i']);
  });
});

has

has<T>(prop: string, obj: T): boolean

It returns true if obj has property prop.

const obj = {a: 1}

const result = [
  R.has('a', obj),
  R.has('b', obj)
]
// => [true, false]

Try the above R.has example in Rambda REPL

All Typescript definitions

has<T>(prop: string, obj: T): boolean;
has(prop: string): <T>(obj: T) => boolean;

R.has source

export function has(prop, obj){
  if (arguments.length === 1) return _obj => has(prop, _obj)

  if (!obj) return false

  return obj[ prop ] !== undefined
}

Tests

import { has } from './has'

test('happy', () => {
  expect(has('a')({ a : 1 })).toBeTrue()
  expect(has('b', { a : 1 })).toBeFalse()
})

test('with non-object', () => {
  expect(has('a', undefined)).toEqual(false)
  expect(has('a', null)).toEqual(false)
  expect(has('a', true)).toEqual(false)
  expect(has('a', '')).toEqual(false)
  expect(has('a', /a/)).toEqual(false)
})

1 failed Ramda.has specs

💥 Reason for the failure: rambda does check properties from the prototype chain

var R = require('../../../../dist/rambda.js');
var eq = require('./shared/eq');

describe('has', function() {
  var fred = {name: 'Fred', age: 23};
  var anon = {age: 99};
  it('does not check properties from the prototype chain', function() {
    var Person = function() {};
    Person.prototype.age = function() {};
    var bob = new Person();
    eq(R.has('age', bob), false);
  });
});

hasPath

hasPath<T>(
  path: string | string[],
  input: object
): boolean

It will return true, if input object has truthy path(calculated with R.path).

const path = 'a.b'
const pathAsArray = ['a', 'b']
const obj = {a: {b: []}}

const result = [
  R.hasPath(path, obj),
  R.hasPath(pathAsArray, obj),
  R.hasPath('a.c', obj),
]
// => [true, true, false]

Try the above R.hasPath example in Rambda REPL

All Typescript definitions

hasPath<T>(
  path: string | string[],
  input: object
): boolean;
hasPath<T>(
  path: string | string[]
): (input: object) => boolean;

R.hasPath source

import { path } from './path'

export function hasPath(maybePath, obj){
  if (arguments.length === 1){
    return objHolder => hasPath(maybePath, objHolder)
  }

  return path(maybePath, obj) !== undefined
}

Tests

import { hasPath } from './hasPath'

test('when true', () => {
  const path = 'a.b'
  const obj = { a : { b : [] } }

  const result = hasPath(path)(obj)
  const expectedResult = true

  expect(result).toEqual(expectedResult)
})

test('when false', () => {
  const path = 'a.b'
  const obj = {}

  const result = hasPath(path, obj)
  const expectedResult = false

  expect(result).toEqual(expectedResult)
})

head

head<T>(listOrString: T[]): T | undefined

It returns the first element of listOrString.

const result = [
  R.head([1, 2, 3]),
  R.head('foo') 
]
// => [1, 'f']

Try the above R.head example in Rambda REPL

All Typescript definitions

head<T>(listOrString: T[]): T | undefined;
head(listOrString: string): string;

R.head source

export function head(listOrString){
  if (typeof listOrString === 'string') return listOrString[ 0 ] || ''

  return listOrString[ 0 ]
}

Tests

import { head } from './head'

test('head', () => {
  expect(head([ 'fi', 'fo', 'fum' ])).toEqual('fi')
  expect(head([])).toEqual(undefined)
  expect(head('foo')).toEqual('f')
  expect(head('')).toEqual('')
})

identical

identical<T>(a: T, b: T): boolean

It returns true if its arguments a and b are identical.

Otherwise, it returns false.

const obj = {a: 1};
R.identical(obj, obj); //=> true
R.identical(1, 1); //=> true
R.identical(1, '1'); //=> false
R.identical([], []); //=> false
R.identical(0, -0); //=> false
R.identical(NaN, NaN); //=> true

Try the above R.identical example in Rambda REPL

All Typescript definitions

identical<T>(a: T, b: T): boolean;
identical<T>(a: T): (b: T) => boolean;

R.identical source

import _objectIs from './_internals/_objectIs'

export function identical(a, b){
  if (arguments.length === 1) return _b => identical(a, _b)

  return _objectIs(a, b)
}

Tests

import { F, T } from '../rambda'
import { _isInteger } from './_internals/_isInteger'
import { _objectIs } from './_internals/_objectIs'
import { identical } from './identical'

test('with boolean', () => {
  expect(F()).toBe(false)
  expect(T()).toBe(true)
})

test('internal isInteger', () => {
  expect(_isInteger(1)).toBe(true)
  expect(_isInteger(0.3)).toBe(false)
})

test('internal objectIs', () => {
  expect(_objectIs(1, 1)).toBe(true)
  expect(_objectIs(NaN, NaN)).toBe(true)
})

test('identical', () => {
  const a = {}

  expect(identical(100)(100)).toEqual(true)
  expect(identical(100, '100')).toEqual(false)
  expect(identical('string', 'string')).toEqual(true)
  expect(identical([], [])).toEqual(false)
  expect(identical(a, a)).toEqual(true)
  expect(identical(undefined, undefined)).toEqual(true)
  expect(identical(null, undefined)).toEqual(false)
})

identity

identity<T>(input: T): T

It just passes back the supplied input argument.

R.identity(7) // => 7

Try the above R.identity example in Rambda REPL

All Typescript definitions

identity<T>(input: T): T;

R.identity source

export function identity(input){
  return input
}

Tests

import { identity } from './identity'

test('happy', () => {
  expect(identity(7)).toEqual(7)
  expect(identity(true)).toEqual(true)
  expect(identity({ a : 1 })).toEqual({ a : 1 })
})

ifElse

ifElse(condition: Pred, onTrue: Arity1Fn, onFalse: Arity1Fn): Arity1Fn

It expects condition, onTrue and onFalse functions as inputs and it returns a new function with example name of fn.

When fn`` is called with inputargument, it will return eitheronTrue(input)oronFalse(input)depending oncondition(input)` evaluation.

const fn = R.ifElse(
 x => x>10,
 x => x*2,
 x => x*10
)

const result = [ fn(8), fn(18) ]
// => [80, 36]

Try the above R.ifElse example in Rambda REPL

All Typescript definitions

ifElse(condition: Pred, onTrue: Arity1Fn, onFalse: Arity1Fn): Arity1Fn;
ifElse(condition: Pred, onTrue: Arity2Fn, onFalse: Arity2Fn): Arity2Fn;

R.ifElse source

import { curry } from './curry'

function ifElseFn(
  condition, onTrue, onFalse
){
  return (...input) => {
    const conditionResult =
      typeof condition === 'boolean' ? condition : condition(...input)

    if (conditionResult === true){
      return onTrue(...input)
    }

    return onFalse(...input)
  }
}

export const ifElse = curry(ifElseFn)

Tests

import { always } from './always'
import { has } from './has'
import { identity } from './identity'
import { ifElse } from './ifElse'
import { prop } from './prop'

const condition = has('foo')
const v = function (a){
  return typeof a === 'number'
}
const t = function (a){
  return a + 1
}
const ifFn = x => prop('foo', x).length
const elseFn = () => false

test('happy', () => {
  const fn = ifElse(condition, ifFn)(elseFn)

  expect(fn({ foo : 'bar' })).toEqual(3)
  expect(fn({ fo : 'bar' })).toEqual(false)
})

test('ramda spec', () => {
  const ifIsNumber = ifElse(v)
  expect(ifIsNumber(t, identity)(15)).toEqual(16)
  expect(ifIsNumber(t, identity)('hello')).toEqual('hello')
})

test('pass all arguments', () => {
  const identity = function (a){
    return a
  }
  const v = function (){
    return true
  }
  const onTrue = function (a, b){
    expect(a).toEqual(123)
    expect(b).toEqual('abc')
  }
  ifElse(
    v, onTrue, identity
  )(123, 'abc')
})

test('accept constant as condition', () => {
  const fn = ifElse(true)(always(true))(always(false))

  expect(fn()).toEqual(true)
})

test('accept constant as condition - case 2', () => {
  const fn = ifElse(
    false, always(true), always(false)
  )

  expect(fn()).toEqual(false)
})

test('curry 1', () => {
  const fn = ifElse(condition, ifFn)(elseFn)

  expect(fn({ foo : 'bar' })).toEqual(3)
  expect(fn({ fo : 'bar' })).toEqual(false)
})

test('curry 2', () => {
  const fn = ifElse(condition)(ifFn)(elseFn)

  expect(fn({ foo : 'bar' })).toEqual(3)
  expect(fn({ fo : 'bar' })).toEqual(false)
})

2 failed Ramda.ifElse specs

💥 Reason for the failure: rambda doesn't return a curried function

var R = require('../../../../dist/rambda.js');
var eq = require('./shared/eq');

describe('ifElse', function() {
  var t = function(a) { return a + 1; };
  var identity = function(a) { return a; };
  var isArray = function(a) { return Object.prototype.toString.call(a) === '[object Array]'; };
  it('returns a function whose arity equals the max arity of the three arguments to `ifElse`', function() {
    function a0() { return 0; }
    function a1(x) { return x; }
    function a2(x, y) { return x + y; }
    eq(R.ifElse(a0, a1, a2).length, 2);
    eq(R.ifElse(a0, a2, a1).length, 2);
    eq(R.ifElse(a1, a0, a2).length, 2);
    eq(R.ifElse(a1, a2, a0).length, 2);
    eq(R.ifElse(a2, a0, a1).length, 2);
    eq(R.ifElse(a2, a1, a0).length, 2);
  });
  it('returns a curried function', function() {
    var v = function(a) { return typeof a === 'number'; };
    var ifIsNumber = R.ifElse(v);
    eq(ifIsNumber(t, identity)(15), 16);
    eq(ifIsNumber(t, identity)('hello'), 'hello');
    var fn = R.ifElse(R.gt, R.subtract, R.add);
    eq(fn(2)(7), 9);
    eq(fn(2, 7), 9);
    eq(fn(7)(2), 5);
    eq(fn(7, 2), 5);
  });
});

ifElseAsync

ifElseAsync<T>(
  condition: Async<any> | Func<any>,
  ifFn: Async<any> | Func<any>,
  elseFn: Async<any> | Func<any>
): Async<T>

Asynchronous version of R.ifElse. Any of condition, ifFn and elseFn can be either asynchronous or synchronous.

const condition = async x => {
  await R.delay(100)
  return x>1
}
const ifFn = async x => {
  await R.delay(100)
  return x+1
}
const elseFn = async x => {
  await R.delay(100)
  return x-1
}

const result = R.ifElseAsync(
  condition,
  ifFn,
  elseFn  
)(1)
// => result resolves to `0`

Try the above R.ifElseAsync example in Rambda REPL

All Typescript definitions

ifElseAsync<T>(
  condition: Async<any> | Func<any>,
  ifFn: Async<any> | Func<any>,
  elseFn: Async<any> | Func<any>
): Async<T>;

R.ifElseAsync source

function createThenable(x){
  return async function (input){
    return x(input)
  }
}

export function ifElseAsync(
  condition, ifFn, elseFn
){
  return input =>
    new Promise((resolve, reject) => {
      const conditionPromise = createThenable(condition)
      const ifFnPromise = createThenable(ifFn)
      const elseFnPromise = createThenable(elseFn)

      conditionPromise(input)
        .then(conditionResult => {
          const promised =
            conditionResult === true ? ifFnPromise : elseFnPromise

          promised(input).then(resolve)
            .catch(reject)
        })
        .catch(reject)
    })
}

Tests

import { delay } from './delay'
import { F } from './F'
import { ifElseAsync } from './ifElseAsync'
import { T } from './T'
import { type } from './type'

test('ok', async () => {
  const condition = async x => {
    const delayed = await delay(x * 80)

    return type(delayed) === 'String'
  }
  const conditionFalse = async x => {
    const delayed = await delay(x * 80)

    return type(delayed) === 'Array'
  }

  const ifFn = async x => {
    await delay(x * 60)

    return true
  }

  const elseFn = async x => {
    await delay(x * 60)

    return false
  }

  const result = await ifElseAsync(
    condition, ifFn, elseFn
  )(7)

  const resultFalse = await ifElseAsync(
    conditionFalse, ifFn, elseFn
  )(7)

  expect(result).toBe(true)
  expect(resultFalse).toBe(false)
})

test('works with regular functions', async () => {
  const result = await ifElseAsync(
    async x => type(await delay(x * 80)) === 'String',
    T,
    F
  )(7)

  expect(result).toEqual(true)
})

inc

inc(x: number): number

It increments a number.

R.inc(1) // => 2

Try the above R.inc example in Rambda REPL

All Typescript definitions

inc(x: number): number;

R.inc source

export const inc = x => x + 1

Tests

import { inc } from './inc'

test('happy', () => {
  expect(inc(1)).toBe(2)
})

includes

includes(valueToFind: string, input: ReadonlyArray<string> | string): boolean

If input is string, then this method work as native String.includes.

If input is array, then R.equals is used to define if valueToFind belongs to the list.

const result = [
  R.includes('oo', 'foo'),
  R.includes({a: 1}, [{a: 1}])
]
// => [true, true ]

Try the above R.includes example in Rambda REPL

All Typescript definitions

includes(valueToFind: string, input: ReadonlyArray<string> | string): boolean;
includes(valueToFind: string): (input: ReadonlyArray<string> | string) => boolean;
includes<T>(valueToFind: T, input: ReadonlyArray<T>): boolean;
includes<T>(valueToFind: T): (input: ReadonlyArray<T>) => boolean;

R.includes source

import { _isArray } from './_internals/_isArray'
import { equals } from './equals'

export function includes(valueToFind, input){
  if (arguments.length === 1) return _input => includes(valueToFind, _input)

  if (typeof input === 'string'){
    return input.includes(valueToFind)
  }
  if (!_isArray(input)) return false

  let index = -1

  while (++index < input.length){
    if (equals(input[ index ], valueToFind)){
      return true
    }
  }

  return false
}

Tests

import R from 'ramda'

import { includes } from './includes'

test('includes with string', () => {
  const str = 'more is less'

  expect(includes('less')(str)).toBeTrue()
  expect(R.includes('less')(str)).toBeTrue()
  expect(includes('never', str)).toBeFalse()
  expect(R.includes('never', str)).toBeFalse()
})

test('includes with array', () => {
  const arr = [ 1, 2, 3 ]

  expect(includes(2)(arr)).toBeTrue()
  expect(R.includes(2)(arr)).toBeTrue()

  expect(includes(4, arr)).toBeFalse()
  expect(R.includes(4, arr)).toBeFalse()
})

test('return false if input is falsy', () => {
  expect(includes(2, null)).toBeFalse()
  expect(() => R.includes(2, null)).toThrowWithMessage(TypeError,
    'Cannot read property \'indexOf\' of null')
  expect(includes(4, undefined)).toBeFalse()
  expect(() => R.includes(4, undefined)).toThrowWithMessage(TypeError,
    'Cannot read property \'indexOf\' of undefined')
})

1 failed Ramda.includes specs

💥 Reason for the failure: ramda method pass to equals method if available

var R = require('../../../../dist/rambda.js');
var eq = require('./shared/eq');

describe('includes', function() {
  it('has R.equals semantics', function() {
    function Just(x) { this.value = x; }
    Just.prototype.equals = function(x) {
      return x instanceof Just && R.equals(x.value, this.value);
    };
    eq(R.includes(0, [-0]), false);
    eq(R.includes(-0, [0]), false);
    eq(R.includes(NaN, [NaN]), true);
    eq(R.includes(new Just([42]), [new Just([42])]), true);
  });
});

indexBy

indexBy<T>(condition: (x: T) => string, list: ReadonlyArray<T>): { [key: string]: T }

It generates object with properties provided by condition and values provided by list array.

If condition is a function, then all list members are passed through it.

If condition is a string, then all list members are passed through R.path(condition).

const list = [ {id: 10}, {id: 20} ]

const withFunction = R.indexBy(
  x => x.id,
  list
)
const withString = R.indexBy(
  'id',
  list
)
const result = [
  withFunction, 
  R.equals(withFunction, withString)
]
// => [ { 10: {id: 10}, 20: {id: 20} }, true ]

Try the above R.indexBy example in Rambda REPL

All Typescript definitions

indexBy<T>(condition: (x: T) => string, list: ReadonlyArray<T>): { [key: string]: T };
indexBy<T>(condition: string, list: ReadonlyArray<T>): { [key: string]: T };
indexBy<T>(condition: (x: T) => string): (list: ReadonlyArray<T>) => { [key: string]: T };
indexBy<T>(condition: string): (list: ReadonlyArray<T>) => { [key: string]: T };

R.indexBy source

import { path } from './path'

function indexByPath(pathInput, list){
  const toReturn = {}
  for (let i = 0; i < list.length; i++){
    const item = list[ i ]
    toReturn[ path(pathInput, item) ] = item
  }

  return toReturn
}

export function indexBy(condition, list){
  if (arguments.length === 1){
    return _list => indexBy(condition, _list)
  }

  if (typeof condition === 'string'){
    return indexByPath(condition, list)
  }

  const toReturn = {}
  for (let i = 0; i < list.length; i++){
    const item = list[ i ]
    toReturn[ condition(item) ] = item
  }

  return toReturn
}

Tests

import { indexBy } from './indexBy'
import { prop } from './prop'

test('happy', () => {
  const list = [
    { id : 1 },
    {
      id : 1,
      a  : 2,
    },
    { id : 2 },
    { id : 10 },
    { id : 'a' },
  ]

  expect(indexBy(prop('id'))(list)).toEqual({
    1 : {
      id : 1,
      a  : 2,
    },
    2  : { id : 2 },
    10 : { id : 10 },
    a  : { id : 'a' },
  })
})

test('with string as condition', () => {
  const list = [ { id : 1 }, { id : 2 }, { id : 10 }, { id : 'a' } ]
  const standardResult = indexBy(obj => obj.id, list)
  const suggestionResult = indexBy('id', list)

  expect(standardResult).toEqual(suggestionResult)
})

test('with string - bad path', () => {
  const list = [
    {
      a : {
        b : 1,
        c : 2,
      },
    },
    { a : { c : 4 } },
    {},
    {
      a : {
        b : 10,
        c : 20,
      },
    },
  ]

  const result = indexBy('a.b', list)
  const expected = {
    1 : {
      a : {
        b : 1,
        c : 2,
      },
    },
    10 : {
      a : {
        b : 10,
        c : 20,
      },
    },
    undefined : {},
  }

  expect(result).toEqual(expected)
})

Typescript test

import {indexBy} from 'rambda'

const list = [{a: {b: '1'}}, {a: {c: '2'}}, {a: {b: '3'}}]

describe('indexBy', () => {
  it('happy', () => {
    const result = indexBy<any>(x => x.a.b, list)
    const resultCurried = indexBy<any>(x => x.a.b)(list)
    result // $ExpectType { [key: string]: any; }
    resultCurried // $ExpectType { [key: string]: any; }
  })

  it('with string', () => {
    const result = indexBy<any>('a.b', list)
    const resultCurried = indexBy<any>('a.b')(list)
    result // $ExpectType { [key: string]: any; }
    resultCurried // $ExpectType { [key: string]: any; }
  })

  it('with interface', () => {
    interface Foo {
      a: string,
    }
    const interfaceList = [{a: 'foo'}, {a: 'bar'}]
    const result = indexBy<Foo>(x => {
      x.a // $ExpectType string
      return x.a
    }, interfaceList)
    const resultCurried = indexBy<Foo>(x => {
      x.a // $ExpectType string
      return x.a
    })(interfaceList)
    result // $ExpectType { [key: string]: Foo; }
    resultCurried // $ExpectType { [key: string]: Foo; }
  })
})

1 failed Ramda.indexBy specs

💥 Reason for the failure: ramda method can act as a transducer

var R = require('../../../../dist/rambda.js');
var eq = require('./shared/eq');

describe('indexBy', function() {
  it('can act as a transducer', function() {
    var list = [{id: 'xyz', title: 'A'}, {id: 'abc', title: 'B'}];
    var transducer = R.compose(
      R.indexBy(R.prop('id')),
      R.map(R.pipe(
        R.adjust(0, R.toUpper),
        R.adjust(1, R.omit(['id']))
      )));
    var result = R.into({}, transducer, list);
    eq(result, {ABC: {title: 'B'}, XYZ: {title: 'A'}});
  });
});

indexOf

indexOf<T>(valueToFind: T, list: ReadonlyArray<T>): number

It returns the index of the first element of list equals to valueToFind.

If there is no such element, it returns -1.

const list = [0, 1, 2, 3]

const result = [
  R.indexOf(2, list),
  R.indexOf(0, list)
]
// => [2, -1]

Try the above R.indexOf example in Rambda REPL

All Typescript definitions

indexOf<T>(valueToFind: T, list: ReadonlyArray<T>): number;
indexOf<T>(valueToFind: T): (list: ReadonlyArray<T>) => number;

R.indexOf source

export function indexOf(valueToFind, list){
  if (arguments.length === 1){
    return _list => indexOf(valueToFind, _list)
  }

  let index = -1
  const { length } = list

  while (++index < length){
    if (list[ index ] === valueToFind){
      return index
    }
  }

  return -1
}

Tests

import { indexOf } from './indexOf'

test('indexOf', () => {
  expect(indexOf(3, [ 1, 2, 3, 4 ])).toEqual(2)

  expect(indexOf(10)([ 1, 2, 3, 4 ])).toEqual(-1)
})

2 failed Ramda.indexOf specs

💥 Reason for the failure: ramda method dispatches to indexOf method

var R = require('../../../../dist/rambda.js');
var eq = require('./shared/eq');

describe('indexOf', function() {
  var input = [1, 2, 3, 4, 5];
  var list = [1, 2, 3];
  list[-2] = 4; // Throw a wrench in the gears by assigning a non-valid array index as object property.
  it('has R.equals semantics', function() {
    function Just(x) { this.value = x; }
    Just.prototype.equals = function(x) {
      return x instanceof Just && R.equals(x.value, this.value);
    };
    eq(R.indexOf(0, [-0]), -1);
    eq(R.indexOf(-0, [0]), -1);
    eq(R.indexOf(NaN, [NaN]), 0);
    eq(R.indexOf(new Just([42]), [new Just([42])]), 0);
  });
  it('dispatches to `indexOf` method', function() {
    function Empty() {}
    Empty.prototype.indexOf = R.always(-1);
    function List(head, tail) {
      this.head = head;
      this.tail = tail;
    }
    List.prototype.indexOf = function(x) {
      var idx = this.tail.indexOf(x);
      return this.head === x ? 0 : idx >= 0 ? 1 + idx : -1;
    };
    var list = new List('b',
      new List('a',
        new List('n',
          new List('a',
            new List('n',
              new List('a',
                new Empty()
              )
            )
          )
        )
      )
    );
    eq(R.indexOf('a', 'banana'), 1);
    eq(R.indexOf('x', 'banana'), -1);
    eq(R.indexOf('a', list), 1);
    eq(R.indexOf('x', list), -1);
  });
});

init

init<T>(listOrString: ReadonlyArray<T>): T[]

It returns all but the last element of listOrString.

const result = [
  R.init([1, 2, 3]) , 
  R.init('foo')  // => 'fo'
]
// => [[1, 2], 'fo']

Try the above R.init example in Rambda REPL

All Typescript definitions

init<T>(listOrString: ReadonlyArray<T>): T[];
init(listOrString: string): string;

R.init source

import baseSlice from './_internals/baseSlice'

export function init(listOrString){
  if (typeof listOrString === 'string') return listOrString.slice(0, -1)

  return listOrString.length ? baseSlice(
    listOrString, 0, -1
  ) : []
}

Tests

import { init } from './init'

test('with array', () => {
  expect(init([ 1, 2, 3 ])).toEqual([ 1, 2 ])
  expect(init([ 1, 2 ])).toEqual([ 1 ])
  expect(init([ 1 ])).toEqual([])
  expect(init([])).toEqual([])
  expect(init([])).toEqual([])
  expect(init([ 1 ])).toEqual([])
})

test('with string', () => {
  expect(init('foo')).toEqual('fo')
  expect(init('f')).toEqual('')
  expect(init('')).toEqual('')
})

intersection

intersection<T>(listA: ReadonlyArray<T>, listB: ReadonlyArray<T>): T[]

It loops throw listA and listB and returns the intersection of the two according to R.equals.

const listA = [ { id : 1 }, { id : 2 }, { id : 3 }, { id : 4 } ]
const listB = [ { id : 3 }, { id : 4 }, { id : 5 }, { id : 6 } ]

const result = intersection(listA, listB)
// => [{ id : 3 }, { id : 4 }]

Try the above R.intersection example in Rambda REPL

All Typescript definitions

intersection<T>(listA: ReadonlyArray<T>, listB: ReadonlyArray<T>): T[];
intersection<T>(listA: ReadonlyArray<T>): (listB: ReadonlyArray<T>) => T[];

R.intersection source

import { filter } from './filter'
import { includes } from './includes'

export function intersection(listA, listB){
  if (arguments.length === 1) return _list => intersection(listA, _list)

  return filter(value => includes(value, listB), listA)
}

Tests

import { intersection } from './intersection'

test('intersection', () => {
  const list1 = [ 1, 2, 3, 4 ]
  const list2 = [ 3, 4, 5, 6 ]
  expect(intersection(list1)(list2)).toEqual([ 3, 4 ])

  expect(intersection([], [])).toEqual([])
})

test('intersection with objects', () => {
  const list1 = [ { id : 1 }, { id : 2 }, { id : 3 }, { id : 4 } ]
  const list2 = [ { id : 3 }, { id : 4 }, { id : 5 }, { id : 6 } ]
  expect(intersection(list1)(list2)).toEqual([ { id : 3 }, { id : 4 } ])
})

intersperse

intersperse<T>(separator: T, list: ReadonlyArray<T>): T[]

It adds a separator between members of list.

const list = [ 0, 1, 2, 3 ]
const separator = '|'
const result = intersperse(separator, list)
// => [0, '|', 1, '|', 2, '|', 3]

Try the above R.intersperse example in Rambda REPL

All Typescript definitions

intersperse<T>(separator: T, list: ReadonlyArray<T>): T[];
intersperse<T>(separator: T): (list: ReadonlyArray<T>) => T[];

R.intersperse source

export function intersperse(separator, list){
  if (arguments.length === 1) return _list => intersperse(separator, _list)

  let index = -1
  const len = list.length
  const willReturn = []

  while (++index < len){
    if (index === len - 1){
      willReturn.push(list[ index ])
    } else {
      willReturn.push(list[ index ], separator)
    }
  }

  return willReturn
}

Tests

import { intersperse } from './intersperse'

test('intersperse', () => {
  const list = [ { id : 1 }, { id : 2 }, { id : 10 }, { id : 'a' } ]
  expect(intersperse('!', list)).toEqual([
    { id : 1 },
    '!',
    { id : 2 },
    '!',
    { id : 10 },
    '!',
    { id : 'a' },
  ])

  expect(intersperse('!')([])).toEqual([])
})

is

is(targetPrototype: any, x: any): boolean

It returns true is x is instance of targetPrototype.

const result = [
  R.is(String, 'foo'),  
  R.is(Array, 1)
]
// => [true, false]

Try the above R.is example in Rambda REPL

All Typescript definitions

is(targetPrototype: any, x: any): boolean;
is(targetPrototype: any): (x: any) => boolean;

R.is source

export function is(targetPrototype, x){
  if (arguments.length === 1) return _x => is(targetPrototype, _x)

  return (
    x != null && x.constructor === targetPrototype ||
    x instanceof targetPrototype
  )
}

Tests

import { is } from './is'

test('works with built-in types', () => {
  expect(is(Array, undefined)).toBeFalse()
  expect(is(Array)([])).toBeTrue()
  expect(is(Boolean, new Boolean(false))).toBeTrue()
  expect(is(Date, new Date())).toBeTrue()
  expect(is(Function, () => {})).toBeTrue()
  expect(is(Number, new Number(0))).toBeTrue()
  expect(is(Object, {})).toBeTrue()
  expect(is(RegExp, /(?:)/)).toBeTrue()
  expect(is(String, new String(''))).toBeTrue()
})

test('works with user-defined types', () => {
  function Foo(){}
  function Bar(){}
  Bar.prototype = new Foo()

  const foo = new Foo()
  const bar = new Bar()

  expect(is(Foo, foo)).toBeTrue()
  expect(is(Bar, bar)).toBeTrue()
  expect(is(Foo, bar)).toBeTrue()
  expect(is(Bar, foo)).toBeFalse()
})

test('does not coerce', () => {
  expect(is(Boolean, 1)).toBeFalse()
  expect(is(Number, '1')).toBeFalse()
  expect(is(Number, false)).toBeFalse()
})

test('recognizes primitives as their object equivalents', () => {
  expect(is(Boolean, false)).toBeTrue()
  expect(is(Number, 0)).toBeTrue()
  expect(is(String, '')).toBeTrue()
})

test('does not consider primitives to be instances of Object', () => {
  expect(is(Object, false)).toBeFalse()
  expect(is(Object, 0)).toBeFalse()
  expect(is(Object, '')).toBeFalse()
})

isEmpty

isEmpty<T>(x: T): boolean

It returns true is x is empty.

const result = [
  R.isEmpty(''),
  R.isEmpty({ x : 0 })
]
// => [true, false]

Try the above R.isEmpty example in Rambda REPL

All Typescript definitions

isEmpty<T>(x: T): boolean;

R.isEmpty source

import { type } from './type'

export function isEmpty(input){
  const inputType = type(input)
  if ([ 'Undefined', 'NaN', 'Number', 'Null' ].includes(inputType))
    return false
  if (!input) return true

  if (inputType === 'Object'){
    return Object.keys(input).length === 0
  }

  if (inputType === 'Array'){
    return input.length === 0
  }

  return false
}

Tests

import { isEmpty } from './isEmpty'

test('happy', () => {
  expect(isEmpty(undefined)).toEqual(false)
  expect(isEmpty('')).toEqual(true)
  expect(isEmpty(null)).toEqual(false)
  expect(isEmpty(' ')).toEqual(false)
  expect(isEmpty(new RegExp(''))).toEqual(false)
  expect(isEmpty([])).toEqual(true)
  expect(isEmpty([ [] ])).toEqual(false)
  expect(isEmpty({})).toEqual(true)
  expect(isEmpty({ x : 0 })).toEqual(false)
  expect(isEmpty(0)).toEqual(false)
  expect(isEmpty(NaN)).toEqual(false)
  expect(isEmpty([ '' ])).toEqual(false)
})

1 failed Ramda.isEmpty specs

💥 Reason for the failure: ramda supports typed arrays

var R = require('../../../../dist/rambda.js');
var eq = require('./shared/eq');

describe('isEmpty', function() {
  it('returns true for empty typed array', function() {
    eq(R.isEmpty(Uint8Array.from('')), true);
    eq(R.isEmpty(Float32Array.from('')), true);
    eq(R.isEmpty(new Float32Array([])), true);
    eq(R.isEmpty(Uint8Array.from('1')), false);
    eq(R.isEmpty(Float32Array.from('1')), false);
    eq(R.isEmpty(new Float32Array([1])), false);
  });
});

isFalsy

isFalsy(input: any): boolean

It returns true if input is falsy.

const result = [
  R.ifFalsy(null),
  R.ifFalsy(''),
  R.ifFalsy([]),
  R.ifFalsy({})
]
// => [true, true, true, true]

Try the above R.isFalsy example in Rambda REPL

All Typescript definitions

isFalsy(input: any): boolean;

R.isFalsy source

import { type } from './type'

export function isFalsy(x){
  const typeIs = type(x)
  if ([ 'Array', 'String' ].includes(typeIs)) return x.length === 0
  if (typeIs === 'Object') return Object.keys(x).length === 0
  if ([ 'Null', 'Undefined' ].includes(typeIs)) return true

  return false
}

Tests

import { isFalsy } from './isFalsy'

test('when function', () => {
  expect(isFalsy(() => {})).toBeFalsy()
})

test('when empty string', () => {
  expect(isFalsy('')).toBeTruthy()
})

test('when empty object', () => {
  expect(isFalsy({})).toBeTruthy()
})

test('when null', () => {
  expect(isFalsy(null)).toBeTruthy
})

isFunction

isFunction(input: any): boolean

It returns true if R.type of input is Async or Function.

const result = [
  R.isFunction(R.mapAsync),
  R.isFunction(R.add),
]
// => [true, true]

Try the above R.isFunction example in Rambda REPL

All Typescript definitions

isFunction(input: any): boolean;

R.isFunction source

import { type } from './type'

export function isFunction(fn){
  return [ 'Async', 'Function' ].includes(type(fn))
}

Tests

import { isFunction } from './isFunction'

test('when function', () => {
  const fn = () => {}

  expect(isFunction(fn)).toEqual(true)
})

test('when promise', () => {
  const fn = Promise.resolve(2)

  expect(isFunction(fn)).toBeFalse()
})

test('when async', () => {
  const fn = async x => x

  expect(isFunction(fn)).toEqual(true)
})

test('when false', () => {
  expect(isFunction(null)).toEqual(false)
})

isNil

isNil(x: any): x is null | undefined

It returns true is x is either null or undefined.

const result = [
  R.isNil(null),
  R.isNil(1),
]
// => [true, false]

Try the above R.isNil example in Rambda REPL

All Typescript definitions

isNil(x: any): x is null | undefined;

R.isNil source

export function isNil(x){
  return x === undefined || x === null
}

Tests

import { isNil } from './isNil'

test('happy', () => {
  expect(isNil(null)).toBeTrue()

  expect(isNil(undefined)).toBeTrue()

  expect(isNil([])).toBeFalse()
})

isPromise

isPromise(input: any): boolean

All Typescript definitions

isPromise(input: any): boolean;

isTruthy

isTruthy(input: any): boolean

It returns true if input is truthy.

const result = [
  R.isTruthy([]),
  R.isTruthy({}),
  R.isTruthy([1]),
  R.isTruthy({a: 1})
]
// => [false, false, true, true]

Try the above R.isTruthy example in Rambda REPL

All Typescript definitions

isTruthy(input: any): boolean;

isType

isType(targetType: RambdaTypes, input: any): boolean

It returns true if targetType is equal to type of input according to R.type.

R.isType('Async',R.delay(1000))
// => true

Try the above R.isType example in Rambda REPL

All Typescript definitions

isType(targetType: RambdaTypes, input: any): boolean;
isType(targetType: RambdaTypes): (input: any) => boolean;

R.isType source

import { type } from './type'

export function isType(xType, x){
  if (arguments.length === 1){
    return xHolder => isType(xType, xHolder)
  }

  return type(x) === xType
}

Tests

import { isType } from './isType'

const list = [ 1, 2, 3 ]

test('array', () => {
  expect(isType('Array', list)).toBeTruthy()
  expect(isType('Array')([])).toBeTruthy()
})

test('promise', () => {
  expect(isType('Promise', Promise.resolve(1))).toBeTruthy()
})

isValid

isValid({input: object, schema: Schema}): boolean

It checks if input is following schema specifications.

If validation fails, it returns false.

Please check the detailed explanation as it is hard to write a short description of this method.

Independently, somebody else came with very similar idea called superstruct

R.isType('Promise',Promise.resolve(1))
// => true
const input = { a: ['foo', 'bar'] }
const invalidInput = { a: ['foo', 'bar', 1] }
const schema = {a: ['string'] }
const result = [
  R.isValid({schema, input}),
  R.isValid({schema, invalidInput}),
]
// => [true, false]

Try the above R.isValid example in Rambda REPL

All Typescript definitions

isValid({input: object, schema: Schema}): boolean;

R.isValid source

import { _isArray } from './_internals/_isArray'
import { all } from './all'
import { any } from './any'
import { includes } from './includes'
import { init } from './init'
import { test } from './test'
import { toLower } from './toLower'
import { type } from './type'

export function isPrototype(input){
  const currentPrototype = input.prototype
  const list = [ Number, String, Boolean, Promise ]
  let toReturn = false
  let counter = -1
  while (++counter < list.length && !toReturn){
    if (currentPrototype === list[ counter ].prototype) toReturn = true
  }

  return toReturn
}

export function prototypeToString(input){
  const currentPrototype = input.prototype
  const list = [ Number, String, Boolean, Promise ]
  const translatedList = [ 'Number', 'String', 'Boolean', 'Promise' ]
  let found
  let counter = -1

  while (++counter < list.length){
    if (currentPrototype === list[ counter ].prototype) found = counter
  }

  return translatedList[ found ]
}

const typesWithoutPrototype = [ 'any', 'promise', 'async', 'function' ]

export function fromPrototypeToString(rule){
  if (
    _isArray(rule) ||
    rule === undefined ||
    rule === null ||
    rule.prototype === undefined ||
    typesWithoutPrototype.includes(rule)
  ){
    return {
      rule,
      parsed : false,
    }
  }
  if (String.prototype === rule.prototype){
    return {
      rule   : 'string',
      parsed : true,
    }
  }
  if (Boolean.prototype === rule.prototype){
    return {
      rule   : 'boolean',
      parsed : true,
    }
  }
  if (Number.prototype === rule.prototype){
    return {
      rule   : 'number',
      parsed : true,
    }
  }

  return {
    rule   : type(rule.prototype).toLowerCase(),
    parsed : true,
  }
}

function getRuleAndType(schema, requirementRaw){
  const ruleRaw = schema[ requirementRaw ]
  const typeIs = type(ruleRaw)
  const { rule, parsed } = fromPrototypeToString(ruleRaw)

  return {
    rule     : rule,
    ruleType : parsed ? 'String' : typeIs,
  }
}

export function isValid({ input, schema }){
  if (input === undefined || schema === undefined) return false

  let flag = true
  const boom = boomFlag => {
    if (!boomFlag){
      flag = false
    }
  }

  for (const requirementRaw in schema){
    if (flag){
      const isOptional = requirementRaw.endsWith('?')
      const requirement = isOptional ? init(requirementRaw) : requirementRaw

      const { rule, ruleType } = getRuleAndType(schema, requirementRaw)
      const inputProp = input[ requirement ]
      const inputPropType = type(input[ requirement ])

      const ok = isOptional && inputProp !== undefined || !isOptional

      if (!ok || rule === 'any' && inputProp != null || rule === inputProp)
        continue

      if (ruleType === 'Object'){
        /**
         * This rule is standalone schema, so we recursevly call `isValid`
         */
        const isValidResult = isValid({
          input  : inputProp,
          schema : rule,
        })
        boom(isValidResult)
      } else if (ruleType === 'String'){
        /**
         * Rule is actual rule such as 'number', so the two types are compared
         */
        boom(toLower(inputPropType) === rule)
      } else if (typeof rule === 'function'){
        /**
         * Rule is function so we pass to it the input
         */
        boom(rule(inputProp))
      } else if (ruleType === 'Array' && inputPropType === 'String'){
        /**
         * Enum case | rule is like a: ['foo', 'bar']
         */
        boom(includes(inputProp, rule))
      } else if (
        ruleType === 'Array' &&
        rule.length === 1 &&
        inputPropType === 'Array'
      ){
        /**
         * 1. array of type | rule is like a: ['number']
         * 2. rule is like a: [{foo: 'string', bar: 'number'}]
         */
        const [ currentRule ] = rule
        const currentRuleType = type(currentRule)

        //Check if rule is invalid
        boom(currentRuleType === 'String' ||
            currentRuleType === 'Object' ||
            isPrototype(currentRule))

        if (currentRuleType === 'Object' && flag){
          /**
           * 2. rule is like a: [{from: 'string'}]
           */
          const isValidResult = all(inputPropInstance =>
            isValid({
              input  : inputPropInstance,
              schema : currentRule,
            }),
          inputProp)
          boom(isValidResult)
        } else if (flag){
          /**
           * 1. array of type
           */

          const actualRule =
            currentRuleType === 'String' ?
              currentRule :
              prototypeToString(currentRule)
          const isInvalidResult = any(inputPropInstance =>
            type(inputPropInstance).toLowerCase() !==
              actualRule.toLowerCase(),
          inputProp)
          boom(!isInvalidResult)
        }
      } else if (ruleType === 'RegExp' && inputPropType === 'String'){
        boom(test(rule, inputProp))
      } else {
        boom(false)
      }
    }
  }

  return flag
}

Tests

import { delay } from './delay'
import { isPrototype, isValid } from './isValid'

test('is prototype', () => {
  expect(isPrototype(Promise)).toBe(true)
  expect(isPrototype(Number)).toBe(true)
  expect(isPrototype(Boolean)).toBe(true)
  expect(isPrototype(String)).toBe(true)
  expect(isPrototype(0)).toBe(false)
})

test('prototype inside array', () => {
  const input = { a : [ 1, 2, 3, 4 ] }
  const schema = { a : [ Number ] }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('with Promise prototype', () => {
  const input = { a : [ delay(1), delay(2) ] }
  const schema = { a : [ Promise ] }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('object prototype as rule - true', () => {
  const input = { a : {} }
  const schema = { a : Object }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('list of functions', () => {
  const input = { a : [ () => {}, delay ] }
  const schema = { a : [ 'function' ] }

  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('function schema type can be only string', () => {
  const input = { a : [ () => {}, delay ] }
  const schema = { a : [ Function ] }

  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('object prototype as rule - false', () => {
  const input = { a : null }
  const schema = { a : Object }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('number prototype as rule - true', () => {
  const input = { a : 1 }
  const schema = { a : Number }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('array prototype as rule - true', () => {
  const input = { a : [ 1, 2, 3 ] }
  const schema = { a : Array }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('array prototype as rule - false', () => {
  const input = { a : null }
  const schema = { a : Array }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('string prototype as rule - true', () => {
  const input = { a : 'foo' }
  const schema = { a : String }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('string prototype as rule - false', () => {
  const input = { a : null }
  const schema = { a : String }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('boolean prototype as rule - true', () => {
  const input = { a : true }
  const schema = { a : Boolean }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('boolean prototype as rule - false', () => {
  const input = { a : null }
  const schema = { a : Boolean }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('regex prototype cannot be rule - true', () => {
  const input = { a : /foo/g }
  const schema = { a : new RegExp('foo') }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('undefined as a rule - true', () => {
  const input = { a : undefined }
  const schema = { a : undefined }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('undefined as a rule - false', () => {
  const input = { a : null }
  const schema = { a : undefined }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('null as a rule - true', () => {
  const input = { a : null }
  const schema = { a : null }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('null as a rule - false', () => {
  const input = { a : undefined }
  const schema = { a : null }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('`any` safeguard against `null`', () => {
  const input = { a : null }
  const schema = { a : 'any' }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('`any` safeguard against `undefined`', () => {
  const input = { a : undefined }
  const schema = { a : 'any' }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('type can be `"any"`', () => {
  const input = { a : () => {} }
  const schema = { a : 'any' }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('type can be `"function"`', () => {
  const input = { a : () => {} }
  const schema = { a : 'function' }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('type can be `async`', () => {
  const input = { a : async () => {} }
  const schema = { a : 'async' }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('type can be `promise`', () => {
  const input = { a : delay(1999) }
  const schema = { a : 'promise' }
  // TODO
  // ============================================
  // const schema = { a : Promise }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('type can be `promise` list', () => {
  const input = { a : [ delay(1999) ] }
  const schema = { a : [ 'promise' ] }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('function as schema - false', () => {
  const input = {
    a : {
      ab : () => true,
      ac : 3,
    },
    c : [ 1, 2 ],
  }
  const schema = {
    'a' : {
      ab : /fo/,
      ac : 'number',
    },
    'b?' : 'string',
    'c'  : [ 'number' ],
  }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('regex ok', () => {
  const input = {
    a : {
      ab : 'foo',
      ac : 3,
    },
    c : [ 1, 2 ],
  }
  const schema = {
    'a' : {
      ab : /fo/,
      ac : 'number',
    },
    'b?' : 'string',
    'c'  : [ 'number' ],
  }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('regex !ok', () => {
  const input = {
    a : {
      ab : 'foo',
      ac : 3,
    },
    c : [ 1, 2 ],
  }
  const schema = {
    'a' : {
      ab : /ba/,
      ac : 'number',
    },
    'b?' : 'string',
    'c'  : [ 'number' ],
  }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('optional props is missing', () => {
  const input = {
    a : {
      ab : 'foo',
      ac : 3,
    },
    c : [ 1, 2 ],
  }
  const schema = {
    'a' : {
      ab : 'string',
      ac : 'number',
    },
    'b?' : 'string',
    'c'  : [ 'number' ],
  }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('optional props is wrong type', () => {
  const input = {
    a : {
      ab : 'foo',
      ac : 3,
    },
    b : [],
    c : [ 1, 2 ],
  }
  const schema = {
    'a' : {
      ab : 'string',
      ac : 'number',
    },
    'b?' : 'string',
    'c'  : [ 'number' ],
  }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('optional props - nested', () => {
  const input = {
    a : {
      ab : 'foo',
      ac : 3,
    },
    b : [],
    c : [ 1, 2 ],
  }
  const schema = {
    a : {
      'ab'  : 'string',
      'ac?' : 'number',
    },
    b : 'array',
    c : [ 'number' ],
  }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('optional props is missing - nested', () => {
  const input = {
    a : { ab : 'foo' },
    b : [],
    c : [ 1, 2 ],
  }
  const schema = {
    a : {
      'ab'  : 'string',
      'ac?' : 'number',
    },
    b : 'array',
    c : [ 'number' ],
  }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('optional props is wrong type - nested', () => {
  const input = {
    a : {
      ab : 'foo',
      ac : 'bar',
    },
    b : [],
    c : [ 1, 2 ],
  }
  const schema = {
    a : {
      'ab'  : 'string',
      'ac?' : 'number',
    },
    b : 'array',
    c : [ 'number' ],
  }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('nested schema', () => {
  const input = {
    a : {
      b : 'str',
      c : 3,
      d : 'str',
    },
    b : 'foo',
  }
  const schema = {
    a : {
      b : 'string',
      c : 'number',
      d : 'string',
    },
    b : 'string',
  }

  expect(isValid({
    input,
    schema,
  })).toBeTruthy()

  const invalidInputFirst = {
    a : {
      b : 'str',
      c : 3,
      d : 'str',
    },
    b : 5,
  }

  expect(isValid({
    input : invalidInputFirst,
    schema,
  })).toBeFalsy()

  const invalidInputSecond = {
    a : {
      b : 'str',
      c : 'str',
      d : 'str',
    },
    b : 5,
  }

  expect(isValid({
    input : invalidInputSecond,
    schema,
  })).toBeFalsy()

  const invalidInputThird = {
    a : { b : 'str' },
    b : 5,
  }

  expect(isValid({
    input : invalidInputThird,
    schema,
  })).toBeFalsy()
})

test('array of type', () => {
  const input = {
    a : [ 1, 2 ],
    b : 'foo',
  }
  const schema = {
    a : [ 'number' ],
    b : 'string',
  }

  expect(isValid({
    input,
    schema,
  })).toBeTruthy()

  const invalidInput = {
    a : [ 1, '1' ],
    b : 'foo',
  }

  expect(isValid({
    input : invalidInput,
    schema,
  })).toBeFalsy()
})

test('function as rule', () => {
  const input = {
    a : [ 1, 2, 3, 4 ],
    b : 'foo',
  }
  const invalidInput = {
    a : [ 4 ],
    b : 'foo',
  }

  const schema = {
    a : x => x.length > 2,
    b : 'string',
  }

  expect(isValid({
    input,
    schema,
  })).toBeTruthy()

  expect(isValid({
    input : invalidInput,
    schema,
  })).toBeFalsy()
})

test('input prop is undefined', () => {
  const input = { b : 3 }
  const schema = { a : 'number' }

  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('enum', () => {
  const input = { a : 'foo' }
  const invalidInput = { a : '' }

  const schema = { a : [ 'foo', 'bar', 'baz' ] }

  expect(isValid({
    input,
    schema,
  })).toBeTruthy()

  expect(isValid({
    input : invalidInput,
    schema,
  })).toBeFalsy()
})

test('readme example', () => {
  const basicSchema = { a : [ 'string' ] }
  const schema = {
    b : [ basicSchema ],
    c : {
      d : { e : 'boolean' },
      f : 'array',
    },
    g : [ 'foo', 'bar', 'baz' ],
  }
  const input = {
    b : [ { a : [ 'led', 'zeppelin' ] } ],
    c : {
      d : { e : true },
      f : [ 'any', 1, null, 'value' ],
    },
    g : 'foo',
  }

  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('should allow additional properties', () => {
  const input = {
    title : 'You shook me',
    year  : 1969,
  }

  expect(isValid({
    input,
    schema : { title : 'string' },
  })).toBeTruthy()
})

test('accepts values as schemas', () => {
  const input = {
    title : 'You shook me',
    genre : 'Blues',
    year  : 1969,
  }
  const schema = {
    title : 'You shook me',
    year  : 1969,
  }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('compatible schemas with nested object', () => {
  const input = {
    foo : 'bar',
    baz : { a : { b : 'c' } },
  }
  const invalidInputFirst = {
    foo : 'bar',
    baz : { a : { b : 1 } },
  }
  const invalidInputSecond = {
    foo : 'bar',
    baz : { a : { b : [] } },
  }
  const invalidInputThird = {
    foo : 'bar',
    baz : { a : { b : null } },
  }
  const schema = {
    foo : 'string',
    baz : { a : { b : 'string' } },
  }

  expect(isValid({
    input,
    schema,
  })).toBeTruthy()

  expect(isValid({
    input : invalidInputFirst,
    schema,
  })).toBeFalsy()
  expect(isValid({
    input : invalidInputSecond,
    schema,
  })).toBeFalsy()
  expect(isValid({
    input : invalidInputThird,
    schema,
  })).toBeFalsy()
})

test('should return true when schema is empty object', () => {
  expect(isValid({
    input  : { a : 1 },
    schema : {},
  })).toBeTruthy()
})

test('when schema is undefined', () => {
  expect(isValid({
    input  : { a : 1 },
    schema : undefined,
  })).toBeFalsy()
})

test('should return false with invalid schema rule', () => {
  const input = {
    foo : 'bar',
    a   : {},
  }
  const inputSecond = { foo : 'bar' }

  const schema = {
    foo : 'string',
    baz : { a : {} },
  }

  expect(isValid({
    input,
    schema,
  })).toBeFalsy()

  expect(isValid({
    input : inputSecond,
    schema,
  })).toBeFalsy()
})

test('array of schemas', () => {
  const input = {
    b : [
      {
        a : 'led',
        b : 1,
      },
      {
        a : 'dancing',
        b : 1,
      },
    ],
  }
  const basicSchema = {
    a : String,
    b : Number,
  }
  const schema = { b : [ basicSchema ] }
  const result = isValid({
    input,
    schema,
  })

  expect(result).toBeTruthy()
})

Typescript test

import {isValid} from 'rambda'

describe('isValid', () => {
  it('happy', () => {
    const input = {a: ['foo', 'bar']}
    const schema = {a: ['string']}
    const result = isValid({schema, input})
    result // $ExpectType boolean
  })
})

isValidAsync

isValidAsync(x: IsValidAsync): Promise<boolean>

All Typescript definitions

isValidAsync(x: IsValidAsync): Promise<boolean>;

join

join(x: string, xs: ReadonlyArray<any>): string

It returns a string representing list instances joined with glue.

R.join('-', [1, 2, 3])  // => '1-2-3'

Try the above R.join example in Rambda REPL

All Typescript definitions

join(x: string, xs: ReadonlyArray<any>): string;
join(x: string): (xs: ReadonlyArray<any>) => string;

R.join source

export function join(glue, list){
  if (arguments.length === 1) return _list => join(glue, _list)

  return list.join(glue)
}

Tests

import { join } from './join'

test('curry', () => {
  expect(join('|')([ 'foo', 'bar', 'baz' ])).toEqual('foo|bar|baz')

  expect(join('|', [ 1, 2, 3 ])).toEqual('1|2|3')

  const spacer = join(' ')

  expect(spacer([ 'a', 2, 3.4 ])).toEqual('a 2 3.4')
})

keys

keys<T extends object>(x: T): (keyof T)[]

It applies Object.keys over x and returns its keys.

R.keys({a:1, b:2})  // => ['a', 'b']

Try the above R.keys example in Rambda REPL

All Typescript definitions

keys<T extends object>(x: T): (keyof T)[];
keys<T>(x: T): string[];

R.keys source

export function keys(x){
  return Object.keys(x)
}

Tests

import { keys } from './keys'

test('happy', () => {
  expect(keys({ a : 1 })).toEqual([ 'a' ])
})

1 failed Ramda.keys specs

💥 Reason for the failure: ramda method works for primitives

var R = require('../../../../dist/rambda.js');
var eq = require('./shared/eq');

describe('keys', function() {
  var obj = {a: 100, b: [1, 2, 3], c: {x: 200, y: 300}, d: 'D', e: null, f: undefined};
  function C() { this.a = 100; this.b = 200; }
  C.prototype.x = function() { return 'x'; };
  C.prototype.y = 'y';
  var cobj = new C();
  it('works for primitives', function() {
    eq(R.keys(null), []);
    eq(R.keys(undefined), []);
    eq(R.keys(55), []);
    eq(R.keys('foo'), []);
    eq(R.keys(true), []);
    eq(R.keys(false), []);
    eq(R.keys(NaN), []);
    eq(R.keys(Infinity), []);
    eq(R.keys([]), []);
  });
});

last

last<T>(listOrString: T[]): T | undefined

It returns the last element of listOrString.

const result = [
  R.last([1, 2, 3]),
  R.last('foo'),
]
// => [3, 'o']

Try the above R.last example in Rambda REPL

All Typescript definitions

last<T>(listOrString: T[]): T | undefined;
last(listOrString: string): string;

R.last source

export function last(listOrString){
  if (typeof listOrString === 'string'){
    return listOrString[ listOrString.length - 1 ] || ''
  }

  return listOrString[ listOrString.length - 1 ]
}

Tests

import { last } from './last'

test('happy', () => {
  expect(last([ 'foo', 'bar', 'baz' ])).toEqual('baz')
  expect(last([])).toEqual(undefined)
  expect(last('abc')).toEqual('c')
  expect(last('')).toEqual('')
})

lastIndexOf

lastIndexOf<T>(target: T, list: ReadonlyArray<T>): number

It returns the last index of target in list array.

R.equals is used to determine equality between target and members of list.

If there is no such index, then -1 is returned.

const list = [1, 2, 3, 1, 2, 3]
const result = [
  R.lastIndexOf(2, list),
  R.lastIndexOf(4, list),
]
// => [4, -1]

Try the above R.lastIndexOf example in Rambda REPL

All Typescript definitions

lastIndexOf<T>(target: T, list: ReadonlyArray<T>): number;
lastIndexOf<T>(target: T): (list: ReadonlyArray<T>) => number;

R.lastIndexOf source

import { equals } from './equals'

export function lastIndexOf(target, list){
  if (arguments.length === 1) return _list => lastIndexOf(target, _list)

  let index = list.length

  while (--index > 0){
    if (equals(list[ index ], target)){
      return index
    }
  }

  return -1
}

Tests

import { lastIndexOf } from './lastIndexOf'

test('happy', () => {
  const a = lastIndexOf(1, [ 1, 2, 3, 1, 2 ])
  const b = lastIndexOf(1)([ 1, 2, 3, 1, 2 ])

  expect(a).toEqual(3)
  expect(b).toEqual(3)
})

test('false', () => {
  const a = lastIndexOf(10, [ 1, 2, 3, 1, 2 ])

  expect(a).toEqual(-1)
})

3 failed Ramda.lastIndexOf specs

💥 Reason for the failure: ramda method dispatches to lastIndexOf method

var R = require('../../../../dist/rambda.js');
var eq = require('./shared/eq');

describe('lastIndexOf', function() {
  var input = [1, 2, 3, 4, 5, 1];
  var list = ['a', 1, 'a'];
  list[-2] = 'a'; // Throw a wrench in the gears by assigning a non-valid array index as object property.
  it('has R.equals semantics', function() {
    function Just(x) { this.value = x; }
    Just.prototype.equals = function(x) {
      return x instanceof Just && R.equals(x.value, this.value);
    };
    eq(R.lastIndexOf(0, [-0]), -1);
    eq(R.lastIndexOf(-0, [0]), -1);
    eq(R.lastIndexOf(NaN, [NaN]), 0);
    eq(R.lastIndexOf(new Just([42]), [new Just([42])]), 0);
  });
  it('dispatches to `lastIndexOf` method', function() {
    function Empty() {}
    Empty.prototype.lastIndexOf = R.always(-1);
    function List(head, tail) {
      this.head = head;
      this.tail = tail;
    }
    List.prototype.lastIndexOf = function(x) {
      var idx = this.tail.lastIndexOf(x);
      return idx >= 0 ? 1 + idx : this.head === x ? 0 : -1;
    };
    var list = new List('b',
      new List('a',
        new List('n',
          new List('a',
            new List('n',
              new List('a',
                new Empty()
              )
            )
          )
        )
      )
    );
    eq(R.lastIndexOf('a', 'banana'), 5);
    eq(R.lastIndexOf('x', 'banana'), -1);
    eq(R.lastIndexOf('a', list), 5);
    eq(R.lastIndexOf('x', list), -1);
  });
  it('finds function, compared by identity', function() {
    var f = function() {};
    var g = function() {};
    var list = [g, f, g, f];
    eq(R.lastIndexOf(f, list), 3);
  });
});

length

length<T>(listOrString: ReadonlyArray<T>): number

It returns the length property of listOrString.

const result = [
  R.length([1, 2, 3, 4]),
  R.length('foo'),
]
// => [4, 3]

Try the above R.length example in Rambda REPL

All Typescript definitions

length<T>(listOrString: ReadonlyArray<T>): number;

R.length source

export function length(x){
  if (!x || x.length === undefined){
    return NaN
  }

  return x.length
}

Tests

import { length } from './length'

test('happy', () => {
  expect(length('foo')).toEqual(3)
  expect(length([ 1, 2, 3 ])).toEqual(3)
  expect(length([])).toEqual(0)
})

test('with bad input returns NaN', () => {
  expect(length(0)).toBeNaN()
  expect(length({})).toBeNaN()
  expect(length(null)).toBeNaN()
  expect(length(undefined)).toBeNaN()
})

1 failed Ramda.length specs

💥 Reason for the failure: ramda method supports object with length method

var R = require('../../../../dist/rambda.js');
var eq = require('./shared/eq');

describe('length', function() {
  it('returns the length of a string', function() {
    eq(R.length(''), 0);
    eq(R.length('xyz'), 3);
  });
  it('returns NaN for length property of unexpected type', function() {
    eq(R.identical(NaN, R.length({length: ''})), true);
    eq(R.identical(NaN, R.length({length: '1.23'})), true);
    eq(R.identical(NaN, R.length({length: null})), true);
    eq(R.identical(NaN, R.length({length: undefined})), true);
    eq(R.identical(NaN, R.length({})), true);
  });
});

lens

lens<T, U, V>(getter: (s: T) => U, setter: (a: U, s: T) => V): Lens

It returns a lens for the given getter and setter functions.

The getter gets the value of the focus; the setter sets the value of the focus.

The setter should not mutate the data structure.

const xLens = R.lens(R.prop('x'), R.assoc('x'));

R.view(xLens, {x: 1, y: 2}) // => 1
R.set(xLens, 4, {x: 1, y: 2}) // => {x: 4, y: 2}
R.over(xLens, R.negate, {x: 1, y: 2}) // => {x: -1, y: 2}

Try the above R.lens example in Rambda REPL

All Typescript definitions

lens<T, U, V>(getter: (s: T) => U, setter: (a: U, s: T) => V): Lens;
lens<T, U, V>(getter: (s: T) => U, setter: (a: U, s: T) => V): Lens;

R.lens source

export function lens(getter, setter){
  if (arguments.length === 1) return _setter => lens(getter, _setter)

  return function (functor){
    return function (target){
      return functor(getter(target)).map(focus => setter(focus, target))
    }
  }
}

lensIndex

lensIndex(index: number): Lens

It returns a lens that focuses on specified index.

const list = ['a', 'b', 'c']
const headLens = R.lensIndex(0)

R.view(headLens, list) // => 'a'
R.set(headLens, 'x', list) // => ['x', 'b', 'c']
R.over(headLens, R.toUpper, list) // => ['A', 'b', 'c']

Try the above R.lensIndex example in Rambda REPL

All Typescript definitions

lensIndex(index: number): Lens;

R.lensIndex source

import { lens } from './lens'
import { nth } from './nth'
import { update } from './update'

export function lensIndex(index){
  return lens(nth(index), update(index))
}

Tests

import { compose } from './compose'
import { keys } from './keys'
import { lensIndex } from './lensIndex'
import { over } from './over'
import { set } from './set'
import { view } from './view'

const testList = [ { a : 1 }, { b : 2 }, { c : 3 } ]

test('focuses list element at the specified index', () => {
  expect(view(lensIndex(0), testList)).toEqual({ a : 1 })
})

test('returns undefined if the specified index does not exist', () => {
  expect(view(lensIndex(10), testList)).toEqual(undefined)
})

test('sets the list value at the specified index', () => {
  expect(set(
    lensIndex(0), 0, testList
  )).toEqual([ 0, { b : 2 }, { c : 3 } ])
})

test('applies function to the value at the specified list index', () => {
  expect(over(
    lensIndex(2), keys, testList
  )).toEqual([ { a : 1 }, { b : 2 }, [ 'c' ] ])
})

test('can be composed', () => {
  const nestedList = [ 0, [ 10, 11, 12 ], 1, 2 ]
  const composedLens = compose(lensIndex(1), lensIndex(0))

  expect(view(composedLens, nestedList)).toEqual(10)
})

test('set s (get s) === s', () => {
  expect(set(
    lensIndex(0), view(lensIndex(0), testList), testList
  )).toEqual(testList)
})

test('get (set s v) === v', () => {
  expect(view(lensIndex(0), set(
    lensIndex(0), 0, testList
  ))).toEqual(0)
})

test('get (set(set s v1) v2) === v2', () => {
  expect(view(lensIndex(0),
    set(
      lensIndex(0), 11, set(
        lensIndex(0), 10, testList
      )
    ))).toEqual(11)
})

lensPath

lensPath(path: RamdaPath): Lens

It returns a lens that focuses on specified path.

const lensPath = R.lensPath(['x', 0, 'y'])
const input = {x: [{y: 2, z: 3}, {y: 4, z: 5}]}

R.view(lensPath, input) //=> 2

R.set(lensPath, 1, input) 
//=> {x: [{y: 1, z: 3}, {y: 4, z: 5}]}

R.over(xHeadYLens, R.negate, input) 
//=> {x: [{y: -2, z: 3}, {y: 4, z: 5}]}

Try the above R.lensPath example in Rambda REPL

All Typescript definitions

lensPath(path: RamdaPath): Lens;

R.lensPath source

import { assocPath } from './assocPath'
import { lens } from './lens'
import { path } from './path'

export function lensPath(key){
  return lens(path(key), assocPath(key))
}

Tests

import { compose } from './compose'
import { identity } from './identity'
import { inc } from './inc'
import { lensPath } from './lensPath'
import { lensProp } from './lensProp'
import { over } from './over'
import { set } from './set'
import { view } from './view'

const testObj = {
  a : [ { b : 1 }, { b : 2 } ],
  d : 3,
}

test('view', () => {
  expect(view(lensPath('d'), testObj)).toEqual(3)
  expect(view(lensPath('a.0.b'), testObj)).toEqual(1)
  // this is different to ramda, ramda will return a clone of the input object
  expect(view(lensPath(''), testObj)).toEqual(undefined)
})

test('set', () => {
  expect(set(
    lensProp('d'), 0, testObj
  )).toEqual({
    a : [ { b : 1 }, { b : 2 } ],
    d : 0,
  })
  expect(set(
    lensPath('a.0.b'), 0, testObj
  )).toEqual({
    a : [ { b : 0 }, { b : 2 } ],
    d : 3,
  })
  expect(set(
    lensPath('a.0.X'), 0, testObj
  )).toEqual({
    a : [
      {
        b : 1,
        X : 0,
      },
      { b : 2 },
    ],
    d : 3,
  })
  expect(set(
    lensPath([]), 0, testObj
  )).toEqual(0)
})

test('over', () => {
  expect(over(
    lensPath('d'), inc, testObj
  )).toEqual({
    a : [ { b : 1 }, { b : 2 } ],
    d : 4,
  })
  expect(over(
    lensPath('a.1.b'), inc, testObj
  )).toEqual({
    a : [ { b : 1 }, { b : 3 } ],
    d : 3,
  })
  expect(over(
    lensProp('X'), identity, testObj
  )).toEqual({
    a : [ { b : 1 }, { b : 2 } ],
    d : 3,
    X : undefined,
  })
  expect(over(
    lensPath('a.0.X'), identity, testObj
  )).toEqual({
    a : [
      {
        b : 1,
        X : undefined,
      },
      { b : 2 },
    ],
    d : 3,
  })
})

test('compose', () => {
  const composedLens = compose(lensPath('a'), lensPath('1.b'))
  expect(view(composedLens, testObj)).toEqual(2)
})

test('set s (get s) === s', () => {
  expect(set(
    lensPath([ 'd' ]), view(lensPath([ 'd' ]), testObj), testObj
  )).toEqual(testObj)
  expect(set(
    lensPath([ 'a', 0, 'b' ]),
    view(lensPath([ 'a', 0, 'b' ]), testObj),
    testObj
  )).toEqual(testObj)
})

test('get (set s v) === v', () => {
  expect(view(lensPath([ 'd' ]), set(
    lensPath([ 'd' ]), 0, testObj
  ))).toEqual(0)
  expect(view(lensPath([ 'a', 0, 'b' ]), set(
    lensPath([ 'a', 0, 'b' ]), 0, testObj
  ))).toEqual(0)
})

test('get (set(set s v1) v2) === v2', () => {
  const p = [ 'd' ]
  const q = [ 'a', 0, 'b' ]
  expect(view(lensPath(p), set(
    lensPath(p), 11, set(
      lensPath(p), 10, testObj
    )
  ))).toEqual(11)
  expect(view(lensPath(q), set(
    lensPath(q), 11, set(
      lensPath(q), 10, testObj
    )
  ))).toEqual(11)
})

lensProp

lensProp(prop: string): {
  <T, U>(obj: T): U

It returns a lens that focuses on specified property prop.

const xLens = R.lensProp('x');
const input = {x: 1, y: 2}

R.view(xLens, input) // => 1

R.set(xLens, 4, input) 
// => {x: 4, y: 2}

R.over(xLens, R.negate, input) 
// => {x: -1, y: 2}

Try the above R.lensProp example in Rambda REPL

All Typescript definitions

lensProp(prop: string): {
  <T, U>(obj: T): U;
  set<T, U, V>(val: T, obj: U): V;
};

R.lensProp source

import { assoc } from './assoc'
import { lens } from './lens'
import { prop } from './prop'

export function lensProp(key){
  return lens(prop(key), assoc(key))
}

Tests

import { compose } from './compose'
import { identity } from './identity'
import { inc } from './inc'
import { lensProp } from './lensProp'
import { over } from './over'
import { set } from './set'
import { view } from './view'

const testObj = {
  a : 1,
  b : 2,
  c : 3,
}

test('focuses object the specified object property', () => {
  expect(view(lensProp('a'), testObj)).toEqual(1)
})

test('returns undefined if the specified property does not exist', () => {
  expect(view(lensProp('X'), testObj)).toEqual(undefined)
})

test('sets the value of the object property specified', () => {
  expect(set(
    lensProp('a'), 0, testObj
  )).toEqual({
    a : 0,
    b : 2,
    c : 3,
  })
})

test('adds the property to the object if it doesn\'t exist', () => {
  expect(set(
    lensProp('d'), 4, testObj
  )).toEqual({
    a : 1,
    b : 2,
    c : 3,
    d : 4,
  })
})

test('applies function to the value of the specified object property', () => {
  expect(over(
    lensProp('a'), inc, testObj
  )).toEqual({
    a : 2,
    b : 2,
    c : 3,
  })
})

test('applies function to undefined and adds the property if it doesn\'t exist', () => {
  expect(over(
    lensProp('X'), identity, testObj
  )).toEqual({
    a : 1,
    b : 2,
    c : 3,
    X : undefined,
  })
})

test('can be composed', () => {
  const nestedObj = {
    a : { b : 1 },
    c : 2,
  }
  const composedLens = compose(lensProp('a'), lensProp('b'))

  expect(view(composedLens, nestedObj)).toEqual(1)
})

test('set s (get s) === s', () => {
  expect(set(
    lensProp('a'), view(lensProp('a'), testObj), testObj
  )).toEqual(testObj)
})

test('get (set s v) === v', () => {
  expect(view(lensProp('a'), set(
    lensProp('a'), 0, testObj
  ))).toEqual(0)
})

test('get (set(set s v1) v2) === v2', () => {
  expect(view(lensProp('a'),
    set(
      lensProp('a'), 11, set(
        lensProp('a'), 10, testObj
      )
    ))).toEqual(11)
})

map

map<T, U>(fn: MapFunctionObject<T, U>, list: Dictionary<T>): Dictionary<U>

It returns the result of looping through list with fn.

It works with both array and object.

const fn = (x, i) => (x * 2) + i
const fnWhenObject = (val, prop)=>{
  return `${prop}-${val}`
}

const list = [1, 2]
const obj = {a: 1, b: 2}

const result = [ 
  R.map(fn, list),
  R.map(fnWhenObject, obj)
]
// => [ [2, 5], {a: 'a-1', b: 'b-2'}]

Try the above R.map example in Rambda REPL

All Typescript definitions

map<T, U>(fn: MapFunctionObject<T, U>, list: Dictionary<T>): Dictionary<U>;
map<T, U>(fn: MapFunctionArray<T, U>, list: T[]): U[];
map<T, U>(fn: MapFunctionArray<T, U>): (list: T[]) => U[];
map<T, U, S>(fn: MapFunctionObject<T, U>): (list: Dictionary<T>) => Dictionary<U>;
map<T>(fn: MapFunctionArray<T, T>): (list: T[]) => T[];
map<T>(fn: MapFunctionArray<T, T>, list: ReadonlyArray<T>): T[];

R.map source

import { _isArray } from './_internals/_isArray'
import { _keys } from './_internals/_keys'

export function map(fn, list){
  if (arguments.length === 1) return _list => map(fn, _list)

  if (list === undefined){
    return []
  }

  if (_isArray(list)){
    let index = 0
    const len = list.length
    const willReturn = Array(len)

    while (index < len){
      willReturn[ index ] = fn(list[ index ], index, list)
      index++
    }

    return willReturn
  } else {
    let index = 0
    const keys = _keys(list)
    const len = keys.length
    const willReturn = {}

    while (index < len){
      const key = keys[ index ]
      willReturn[ key ] = fn(list[ key ], key, list)
      index++
    }

    return willReturn
  }
}

Tests

import { map } from './map'

const double = x => x * 2

const sampleObject = {
  a : 1,
  b : 2,
  c : 3,
  d : 4,
}

test('with array', () => {
  expect(map(double, [ 1, 2, 3 ])).toEqual([ 2, 4, 6 ])
})

test('pass index as second argument', () => {
  map((x, i) => {
    expect(i).toBeNumber()
  },
  [ 10, 20, 30 ])
})

test('with object', () => {
  const obj = {
    a : 1,
    b : 2,
  }

  expect(map(double, obj)).toEqual({
    a : 2,
    b : 4,
  })
})

test('pass input object as third argument', () => {
  const obj = {
    a : 1,
    b : 2,
  }
  const iterator = (
    val, prop, inputObject
  ) => {
    expect(inputObject).toEqual(obj)

    return val * 2
  }

  expect(map(iterator, obj)).toEqual({
    a : 2,
    b : 4,
  })
})

test('with object passes property as second argument', () => {
  map((_, prop) => {
    expect(typeof prop).toEqual('string')
  })(sampleObject)
})

/**
 * https://github.com/selfrefactor/rambda/issues/77
 */
test('when undefined instead of array', () => {
  expect(map(double, undefined)).toEqual([])
})

Typescript test

import {map} from 'rambda'

describe('map with arrays', () => {
  it('only one type', () => {
    const x = map<number>(
      (a, b) => {
        a // $ExpectType number
        b // $ExpectType number
        return a + 2
      },
      [1, 2, 3]
    )
    x // $ExpectType number[]
  })
  it('only one type + curry', () => {
    const x = map<number>((a, b) => {
      a // $ExpectType number
      b // $ExpectType number
      return a + 2
    })([1, 2, 3])
    x // $ExpectType number[]
  })
  it('2 types', () => {
    const x = map<number, string>(
      (a, b) => {
        a // $ExpectType number
        b // $ExpectType number
        return `${a}`
      },
      [1, 2, 3]
    )
    x // $ExpectType string[]
  })
  it('2 types + curry', () => {
    const x = map<number, string>((a, b) => {
      a // $ExpectType number
      b // $ExpectType number
      return `${a}`
    })([1, 2, 3])
    x // $ExpectType string[]
  })
})

describe('map with objects', () => {
  it('curry', () => {
    // It requires dummy third typing argument
    // in order to distinguish compared to curry typings for arrays
    // ============================================
    const x = map<number, string, any>((a, b, c) => {
      a // $ExpectType number
      b // $ExpectType string
      c // $ExpectType Dictionary<number>
      return `${a}`
    })({a: 1, b: 2})
    x // $ExpectType Dictionary<string>
  })
  it('1', () => {
    const x = map<number, string>(
      (a, b, c) => {
        a // $ExpectType number
        b // $ExpectType string
        c // $ExpectType Dictionary<number>
        return `${a}`
      },
      {a: 1, b: 2}
    )
    x // $ExpectType Dictionary<string>
  })
  it('2', () => {
    const x = map<number, string>(
      (a, b) => {
        a // $ExpectType number
        b // $ExpectType string
        return `${a}`
      },
      {a: 1, b: 2}
    )
    x // $ExpectType Dictionary<string>
  })
  it('3', () => {
    const x = map<number, string>(
      a => {
        a // $ExpectType number
        return `${a}`
      },
      {a: 1, b: 2}
    )
    x // $ExpectType Dictionary<string>
  })
})

mapAsync

mapAsync<T>(fn: AsyncWithMap<any>, list: any[]): Promise<T[]>

Sequential asynchronous mapping with fn over members of list.

async function fn(x){
  await R.delay(1000)

  return x+1
}

const result = R.mapAsync(fn, [1, 2, 3])
// `result` resolves after 3 seconds to `[2, 3, 4]`

Try the above R.mapAsync example in Rambda REPL

All Typescript definitions

mapAsync<T>(fn: AsyncWithMap<any>, list: any[]): Promise<T[]>;
mapAsync<T>(fn: AsyncWithProp<any>, obj: object): Promise<T[]>;
mapAsync<T>(fn: AsyncWithMap<any>): (list: any[]) => Promise<T[]>;
mapAsync<T>(fn: AsyncWithProp<any>): (obj: object) => Promise<T[]>;

R.mapAsync source

import { _isArray } from './_internals/_isArray'

async function mapAsyncFn(fn, arr){
  if (_isArray(arr)){
    const willReturn = []
    let i = 0
    for (const a of arr){
      willReturn.push(await fn(a, i++))
    }

    return willReturn
  }

  const willReturn = {}
  for (const prop in arr){
    willReturn[ prop ] = await fn(arr[ prop ], prop)
  }

  return willReturn
}

export function mapAsync(fn, arr){
  if (arguments.length === 1){
    return async holder => mapAsyncFn(fn, holder)
  }

  return new Promise((resolve, reject) => {
    mapAsyncFn(fn, arr).then(resolve)
      .catch(reject)
  })
}

Tests

import { composeAsync } from './composeAsync'
import { map } from './map'
import { mapAsync } from './mapAsync'

const delay = a =>
  new Promise(resolve => {
    setTimeout(() => {
      resolve(a + 20)
    }, 100)
  })

const tap = a =>
  new Promise(resolve => {
    setTimeout(() => {
      resolve(a)
    }, 100)
  })

const rejectDelay = a =>
  new Promise((_, reject) => {
    setTimeout(() => {
      reject(a + 20)
    }, 100)
  })

test('', async () => {
  const result = await mapAsync(delay, [ 1, 2, 3 ])
  expect(result).toEqual([ 21, 22, 23 ])
})

test('with object', async () => {
  const result = await mapAsync(delay, {
    a : 1,
    b : 2,
    c : 3,
  })
  expect(result).toEqual({
    a : 21,
    b : 22,
    c : 23,
  })
})

test('with array', async () => {
  await mapAsync((x, i) => {
    expect(x % 10).toBe(0)
    expect(typeof i).toBe('number')
  },
  [ 10, 20, 30 ])
})

test('composeAsync', async () => {
  const result = await composeAsync(
    mapAsync(delay),
    mapAsync(async a => delay(a)),
    map(a => a * 10)
  )(await tap([ 1, 2, 3 ]))
  expect(result).toEqual([ 50, 60, 70 ])
})

test('error', async () => {
  try {
    await mapAsync(rejectDelay)([ 1, 2, 3 ])
  } catch (err){
    expect(err).toBe(21)
  }
})

mapAsyncLimit

mapAsyncLimit<T, U>(fn: (x: T) => Promise<U>, limit: number, list: T[]): Promise<U[]>

It is similar to R.mapFastAsync in that it uses Promise.all but not over the whole list, rather than with only slice from list with length limit.

All Typescript definitions

mapAsyncLimit<T, U>(fn: (x: T) => Promise<U>, limit: number, list: T[]): Promise<U[]>;
mapAsyncLimit<T, U>(fn: (x: T) => Promise<U>, limit: number): (list: T[]) => Promise<U[]>;

R.mapAsyncLimit source

import { mapFastAsync, mapFastAsyncFn } from './mapFastAsync'
import { splitEvery } from './splitEvery'

export async function mapAsyncLimit(
  iterable, limit, list
){
  if (arguments.length === 2){
    return _list => mapAsyncLimit(
      iterable, limit, _list
    )
  }
  if (list.length < limit) return mapFastAsync(iterable, list)

  const slices = splitEvery(limit, list)

  let toReturn = []
  for (const slice of slices){
    const iterableResult = await mapFastAsyncFn(iterable, slice)
    toReturn = [ ...toReturn, ...iterableResult ]
  }

  return toReturn
}

Tests

import isCI from 'is-ci'

import { delay } from './delay'
import { mapAsync } from './mapAsync'
import { mapAsyncLimit } from './mapAsyncLimit'
import { toDecimal } from './toDecimal'

jest.setTimeout(30000)

test('happy', async () => {
  const limit = 3
  const startTime = new Date().getTime()
  const list = [ 1, 2, 3, 4, 5, 6, 7, 8, 9 ]
  const iterable = async x => {
    await delay(500)

    return x + 1
  }
  const result = await mapAsyncLimit(
    iterable, limit, list
  )
  const endTime = new Date().getTime()
  const diffTime = endTime - startTime

  const startTime2 = new Date().getTime()
  await mapAsync(iterable, list)
  const endTime2 = new Date().getTime()
  const diffTime2 = endTime2 - startTime2

  const methodScale = toDecimal((diffTime2 - diffTime) / 1000, 0)
  expect(result).toEqual([ 2, 3, 4, 5, 6, 7, 8, 9, 10 ])
  if (!isCI) expect(methodScale).toBe(limit)
})

mapFastAsync

mapFastAsync<T>(fn: AsyncWithMap<any>, list: any[]): Promise<T[]>

Parrallel asynchronous mapping with fn over members of list.

async function fn(x){
  await R.delay(1000)

  return x+1
}

const result = R.mapFastAsync(fn, [1, 2, 3])
// `result` resolves after 1 second to `[2, 3, 4]`

Try the above R.mapFastAsync example in Rambda REPL

All Typescript definitions

mapFastAsync<T>(fn: AsyncWithMap<any>, list: any[]): Promise<T[]>;
mapFastAsync<T>(fn: AsyncWithProp<any>, obj: object): Promise<T[]>;
mapFastAsync<T>(fn: AsyncWithMap<any>): (list: any[]) => Promise<T[]>;
mapFastAsync<T>(fn: AsyncWithProp<any>): (obj: object) => Promise<T[]>;

R.mapFastAsync source

export async function mapFastAsyncFn(fn, arr){
  const promised = arr.map((a, i) => fn(a, i))

  return Promise.all(promised)
}

export function mapFastAsync(fn, arr){
  if (arguments.length === 1){
    return async holder => mapFastAsyncFn(fn, holder)
  }

  return new Promise((resolve, reject) => {
    mapFastAsyncFn(fn, arr).then(resolve)
      .catch(reject)
  })
}

Tests

import { composeAsync } from './composeAsync'
import { map } from './map'
import { mapFastAsync } from './mapFastAsync'

const delay = a =>
  new Promise(resolve => {
    setTimeout(() => {
      resolve(a + 20)
    }, 100)
  })

const tap = a =>
  new Promise(resolve => {
    setTimeout(() => {
      resolve(a)
    }, 100)
  })

const rejectDelay = a =>
  new Promise((_, reject) => {
    setTimeout(() => {
      reject(a + 20)
    }, 100)
  })

test('happy path', async () => {
  const result = await mapFastAsync(delay, [ 1, 2, 3 ])
  expect(result).toEqual([ 21, 22, 23 ])
})

test('composeAsync', async () => {
  const result = await composeAsync(
    mapFastAsync(async a => delay(a)),
    mapFastAsync(delay),
    map(a => a * 10)
  )(await tap([ 1, 2, 3 ]))
  expect(result).toEqual([ 50, 60, 70 ])
})

test('error', async () => {
  try {
    const result = await mapFastAsync(rejectDelay)([ 1, 2, 3 ])
  } catch (err){
    expect(err).toBe(21)
  }
})

test('with array', async () => {
  await mapFastAsync((x, i) => {
    expect(x % 10).toBe(0)
    expect(typeof i).toBe('number')
  },
  [ 10, 20, 30 ])
})

mapToObject

mapToObject<T, U>(fn: (input: T) => object, list: T[]): U

This method allows to generate an object from a list using input function fn.

This function must return an object for every member of list input. All of the returns will be merged in the final result.

const list = [1, 2, 3]
const fn = x => x%2 ? {[x]: x+1}: {[x]: x+10}

const result = mapToObject(fn, list)
const expected = { '1': 2, '2': 12, '3': 4 }
// => `result` is equal to `expected`

Try the above R.mapToObject example in Rambda REPL

All Typescript definitions

mapToObject<T, U>(fn: (input: T) => object, list: T[]): U;
mapToObject<T, U>(fn: (input: T) => object): (list: T[]) => U;

R.mapToObject source

import { map } from './map'
import { mergeAll } from './mergeAll'
import { ok } from './ok'
import { type } from './type'

export function mapToObject(fn, list){
  if (arguments.length === 1){
    return listHolder => mapToObject(fn, listHolder)
  }
  ok(type(fn), type(list))('Function', 'Array')

  return mergeAll(map(fn, list))
}

Tests

import { mapToObject } from './mapToObject'
import { result } from 'lodash'

test('simple', ()=> {
  const list = [1, 2, 3]
  const fn = x => x%2 ? {[x]: x+1}: {[x]: x+10}
  const result = mapToObject(fn, list)
  const expected = { '1': 2, '2': 12, '3': 4 }

  expect(result).toEqual(expected)
})

test('happy', () => {
  const list = 'auto?bar=false?foo?baz=1.5?s=more?k=2'.split('?')
  const fn = x => {
    const [ key, value ] = x.split('=')
    if (value === undefined || value === 'true'){
      return { [ key ] : true }
    }
    if (value === 'false'){
      return { [ key ] : false }
    }

    if (Number.isNaN(Number(value))){
      return { [ key ] : value }
    }

    return { [ key ] : Number(value) }
  }

  const expectedResult = {
    auto : true,
    foo  : true,
    bar  : false,
    baz  : 1.5,
    s    : 'more',
    k    : 2,
  }
  const result = mapToObject(fn, list)
  const resultx = mapToObject(fn)(list)

  expect(result).toEqual(expectedResult)
  expect(resultx).toEqual(expectedResult)
})

test('bad path', () => {
  expect(() => mapToObject(1, null)).toThrow()
})

match

match(regExpression: RegExp, str: string): any[]

Curried version of String.prototype.match which returns empty array, when there is no match.

const result = [
  R.match('a', 'foo'),
  R.match(/([a-z]a)/g, 'bananas')
]
// => [[], ['ba', 'na', 'na']]

Try the above R.match example in Rambda REPL

All Typescript definitions

match(regExpression: RegExp, str: string): any[];
match(regExpression: RegExp): (str: string) => any[];

R.match source

export function match(pattern, input){
  if (arguments.length === 1) return _input => match(pattern, _input)

  const willReturn = input.match(pattern)

  return willReturn === null ? [] : willReturn
}

Tests

import { equals } from './equals'
import { match } from './match'

test('happy', () => {
  expect(match(/a./g)('foo bar baz')).toEqual([ 'ar', 'az' ])
})

test('fallback', () => {
  expect(match(/a./g)('foo')).toEqual([])
})

test('with string', () => {
  expect(match('a', 'foo')).toEqual([])
  expect(equals(match('o', 'foo'), [ 'o' ])).toBeTrue()
})

test('throwing', () => {
  expect(() => {
    match(/a./g, null)
  }).toThrowWithMessage(TypeError, 'Cannot read property \'match\' of null')
})

mathMod

mathMod(x: number, y: number): number

R.mathMod behaves like the modulo operator should mathematically, unlike the % operator (and by extension, R.modulo). So while -17 % 5 is -2, mathMod(-17, 5) is 3.

const result = [
  R.mathMod(-17, 5),
  R.mathMod(17, 5),
  R.mathMod(17, -5),  
  R.mathMod(17, 0)   
]
// => [3, 2, NaN, NaN]

Try the above R.mathMod example in Rambda REPL

All Typescript definitions

mathMod(x: number, y: number): number;
mathMod(x: number): (y: number) => number;

R.mathMod source

import _isInteger from './_internals/_isInteger'

export function mathMod(x, y){
  if (arguments.length === 1) return _y => mathMod(x, _y)
  if (!_isInteger(x) || !_isInteger(y) || y < 1) return NaN

  return (x % y + y) % y
}

Tests

import { mathMod } from './mathMod'

test('happy', () => {
  expect(mathMod(-17)(5)).toEqual(3)
  expect(mathMod(17, 5)).toEqual(2)
  expect(mathMod(17, -5)).toBeNaN()
  expect(mathMod(17, 0)).toBeNaN()
  expect(mathMod('17', 5)).toBeNaN()
  expect(mathMod({}, 2)).toBeNaN()
  expect(mathMod([], 2)).toBeNaN()
  expect(mathMod(Symbol(), 2)).toBeNaN()
})

max

max<T extends Ord>(x: T, y: T): T

It returns the greater value between x and y.

const result = [
  R.max(5, 7),  
  R.max('bar', 'foo'),  
]
// => [7, 'foo']

Try the above R.max example in Rambda REPL

All Typescript definitions

max<T extends Ord>(x: T, y: T): T;
max<T extends Ord>(x: T): (y: T) => T;

R.max source

export function max(x, y){
  if (arguments.length === 1) return _y => max(x, _y)

  return y > x ? y : x
}

Tests

import { max } from './max'

test('with number', () => {
  expect(max(2, 1)).toBe(2)
})

test('with string', () => {
  expect(max('foo')('bar')).toBe('foo')
  expect(max('bar')('baz')).toBe('baz')
})

maxBy

maxBy<T>(compareFn: (input: T) => Ord, x: T, y: T): T

It returns the greater value between x and y according to compareFn function.

const compareFn = Math.abs

R.maxBy(compareFn, 5, -7) // => -7

Try the above R.maxBy example in Rambda REPL

All Typescript definitions

maxBy<T>(compareFn: (input: T) => Ord, x: T, y: T): T;
maxBy<T>(compareFn: (input: T) => Ord, x: T): (y: T) => T;
maxBy<T>(compareFn: (input: T) => Ord): FunctionToolbelt.Curry<(x: T, y: T) => T>;

R.maxBy source

import { curry } from './curry'

export function maxByFn(
  compareFn, x, y
){
  return compareFn(y) > compareFn(x) ? y : x
}

export const maxBy = curry(maxByFn)

Tests

import { maxBy } from './maxBy'

test('happy', () => {
  expect(maxBy(
    Math.abs, -5, 2
  )).toEqual(-5)
})

test('curried', () => {
  expect(maxBy(Math.abs)(2, -5)).toEqual(-5)
  expect(maxBy(Math.abs)(2)(-5)).toEqual(-5)
})

maybe

maybe<T>(ifRule: any, whenIf: any, whenElse: any): T

It acts as ternary operator and it is helpful when we have nested ternaries.

All of the inputs can be either direct values or anonymous functions. This is helpful if we don't want to evaluate certain paths as we can wrap this logic in a function.

const x = 4
const y = 8

const ifRule = x > 2
const elseRule = y > 10 ? 3 : 7
const whenElse = () => JSON.parse('{a:')

const result = R.maybe(
  ifRule,
  elseRule,
  whenElse,
)
// `result` is `7`

Try the above R.maybe example in Rambda REPL

All Typescript definitions

maybe<T>(ifRule: any, whenIf: any, whenElse: any): T;

R.maybe source

import { type } from './type'

export function maybe(
  ifRule, whenIfRaw, whenElseRaw
){
  const whenIf =
    ifRule && type(whenIfRaw) === 'Function' ? whenIfRaw() : whenIfRaw

  const whenElse =
    !ifRule && type(whenElseRaw) === 'Function' ? whenElseRaw() : whenElseRaw

  return ifRule ? whenIf : whenElse
}

Tests

import { maybe } from './maybe'

const whenIf = 7
const whenElse = 9

test('prevent type error', () => {
  const x = 5
  const y = null
  const ifRule = x > 3

  const result = maybe(
    ifRule, whenIf, () => y.a === 'foo'
  )
  const expectedResult = 7

  expect(result).toEqual(expectedResult)
})

test('function as whenElse', () => {
  const x = 2
  const y = { a : 1 }
  const ifRule = x > 3

  const result = maybe(
    ifRule, whenIf, () => y.a === 'foo'
  )
  const expectedResult = false

  expect(result).toEqual(expectedResult)
})

test('when if', () => {
  const x = 5
  const ifRule = x > 3

  const result = maybe(
    ifRule, whenIf, whenElse
  )
  const expectedResult = 7

  expect(result).toEqual(expectedResult)
})

test('when else', () => {
  const x = 1
  const ifRule = x > 3

  const result = maybe(
    ifRule, whenIf, whenElse
  )
  const expectedResult = 9

  expect(result).toEqual(expectedResult)
})

mean

mean(list: ReadonlyArray<number>): number

It returns the mean value of list input.

R.mean([ 2, 7 ])
// => 4.5

Try the above R.mean example in Rambda REPL

All Typescript definitions

mean(list: ReadonlyArray<number>): number;

R.mean source

import { sum } from './sum'

export function mean(list){
  return sum(list) / list.length
}

Tests

import { mean } from './mean'

test('happy', () => {
  expect(mean([ 2, 7 ])).toBe(4.5)
})

test('with NaN', () => {
  expect(mean([])).toBeNaN()
})

median

median(list: ReadonlyArray<number>): number

It returns the median value of list input.

R.median([ 7, 2, 10, 9 ]) // => 8

Try the above R.median example in Rambda REPL

All Typescript definitions

median(list: ReadonlyArray<number>): number;

R.median source

import { mean } from './mean'

export function median(list){
  const len = list.length
  if (len === 0) return NaN
  const width = 2 - len % 2
  const idx = (len - width) / 2

  return mean(Array.prototype.slice
    .call(list, 0)
    .sort((a, b) => {
      if (a === b) return 0

      return a < b ? -1 : 1
    })
    .slice(idx, idx + width))
}

Tests

import { identical } from './identical'
import { median } from './median'

test('median', () => {
  expect(median([ 2 ])).toEqual(2)
  expect(median([ 7, 2, 10, 9 ])).toEqual(8)
  expect(identical(NaN, median([]))).toBeTrue()
})

memoize

memoize<T>(fn: Func<any> | Async<any>): T

When fn is called for a second time with the same input, then the cache result is returned instead of calling again fn.

let result = 0
const fn = (a,b) =>{
  result++

  return a + b
}
const memoized = R.memoize(fn)
memoized(1, 2)
memoized(1, 2)

// => `result` is equal to `1`

Try the above R.memoize example in Rambda REPL

All Typescript definitions

memoize<T>(fn: Func<any> | Async<any>): T;

R.memoize source

import { compose } from './compose'
import { map } from './map'
import { replace } from './replace'
import { sort } from './sort'
import { take } from './take'
import { type } from './type'

const cache = {}

const normalizeObject = obj => {
  const sortFn = (a, b) => a > b ? 1 : -1
  const willReturn = {}
  compose(map(prop => willReturn[ prop ] = obj[ prop ]),
    sort(sortFn))(Object.keys(obj))

  return willReturn
}

const stringify = a => {
  if (type(a) === 'String'){
    return a
  } else if ([ 'Function', 'Async' ].includes(type(a))){
    const compacted = replace(
      /\s{1,}/g, ' ', a.toString()
    )

    return replace(
      /\s/g, '_', take(15, compacted)
    )
  } else if (type(a) === 'Object'){
    return JSON.stringify(normalizeObject(a))
  }

  return JSON.stringify(a)
}

const generateProp = (fn, ...inputArguments) => {
  let propString = ''
  inputArguments.forEach(inputArgument => {
    propString += `${ stringify(inputArgument) }_`
  })

  return `${ propString }${ stringify(fn) }`
}
// with weakmaps
export function memoize(fn, ...inputArguments){
  if (arguments.length === 1){
    return (...inputArgumentsHolder) => memoize(fn, ...inputArgumentsHolder)
  }

  const prop = generateProp(fn, ...inputArguments)
  if (prop in cache) return cache[ prop ]

  if (type(fn) === 'Async'){
    return new Promise(resolve => {
      fn(...inputArguments).then(result => {
        cache[ prop ] = result
        resolve(result)
      })
    })
  }

  const result = fn(...inputArguments)
  cache[ prop ] = result

  return result
}

Tests

import { memoize } from './memoize'

test('memoize function without input arguments', () => {
  const fn = () => 4
  const memoized = memoize(fn)
  expect(typeof memoized()).toBe('function')
})

test('happy', () => {
  let counter = 0

  const fn = ({ a, b, c }) => {
    counter++

    return a + b - c
  }
  const memoized = memoize(fn)
  expect(memoized({
    a : 1,
    c : 3,
    b : 2,
  })).toBe(0)
  expect(counter).toBe(1)
  expect(memoized({
    c : 3,
    a : 1,
    b : 2,
  })).toBe(0)
  expect(counter).toBe(1)
})

test('normal function', () => {
  let counter = 0
  const fn = (a, b) => {
    counter++

    return a + b
  }
  const memoized = memoize(fn)
  expect(memoized(1, 2)).toBe(3)
  expect(memoized(1, 2)).toBe(3)
  expect(memoized(1, 2)).toBe(3)
  expect(counter).toBe(1)
  expect(memoized(2, 2)).toBe(4)
  expect(counter).toBe(2)
  expect(memoized(1, 2)).toBe(3)
  expect(counter).toBe(2)
})

test('async function', async () => {
  let counter = 0
  const delay = ms =>
    new Promise(resolve => {
      setTimeout(resolve, ms)
    })
  const fn = async (ms, a, b) => {
    await delay(ms)
    counter++

    return a + b
  }

  const memoized = memoize(fn)
  expect(await memoized(
    100, 1, 2
  )).toBe(3)
  expect(await memoized(
    100, 1, 2
  )).toBe(3)
  expect(await memoized(
    100, 1, 2
  )).toBe(3)
  expect(counter).toBe(1)
  expect(await memoized(
    100, 2, 2
  )).toBe(4)
  expect(counter).toBe(2)
  expect(await memoized(
    100, 1, 2
  )).toBe(3)
  expect(counter).toBe(2)
})

test('string as argument', () => {
  let count = 0
  const foo = 'foo'
  const tester = memoize(n => {
    count++

    return `${ n }bar`
  })
  tester(foo)
  tester(foo)
  tester(foo)

  expect(tester(foo)).toEqual('foobar')

  expect(count).toEqual(1)

  tester('baz')

  expect(tester('baz')).toEqual('bazbar')

  expect(count).toEqual(2)
})

merge

merge<O1 extends object, O2 extends object>(target: O1, newProps: O2): Merge<O2, O1, 'flat'>

It creates a copy of target object with overidden newProps properties.

const target = { 'foo': 0, 'bar': 1 }
const newProps = { 'foo': 7 }

const result = R.merge(target, newProps)
// => { 'foo': 7, 'bar': 1 }

Try the above R.merge example in Rambda REPL

All Typescript definitions

merge<O1 extends object, O2 extends object>(target: O1, newProps: O2): Merge<O2, O1, 'flat'>;
merge<O1 extends object>(target: O1): <O2 extends object>(newProps: O2) => Merge<O2, O1, 'flat'>;

R.merge source

export function merge(target, newProps){
  if (arguments.length === 1) return _newProps => merge(target, _newProps)

  return Object.assign(
    {}, target || {}, newProps || {}
  )
}

Tests

import { merge } from './merge'

const sample = {
  foo : 'bar',
  bar : 'bar',
}

test('merge', () => {
  expect(merge(sample)({ bar : 'baz' })).toEqual({
    foo : 'bar',
    bar : 'baz',
  })
})

/**
 * https://github.com/selfrefactor/rambda/issues/77
 */
test('when undefined or null instead of object', () => {
  expect(merge(null, undefined)).toEqual({})
  expect(merge(sample, null)).toEqual(sample)
  expect(merge(sample, undefined)).toEqual(sample)
  expect(merge(undefined, sample)).toEqual(sample)
})

mergeAll

mergeAll(list: object[]): object

It merges all objects of list array sequentially and returns the result.

const list = [
  {a: 1},
  {b: 2},
  {c: 3}
]
const result = R.mergeAll(list)
const expected = {
  a: 1,
  b: 2,
  c: 3
}
// => `result` is equal to `expected`

Try the above R.mergeAll example in Rambda REPL

All Typescript definitions

mergeAll(list: object[]): object;

R.mergeAll source

import { map } from './map'
import { merge } from './merge'

export function mergeAll(arr){
  let willReturn = {}
  map(val => {
    willReturn = merge(willReturn, val)
  }, arr)

  return willReturn
}

Tests

import { mergeAll } from './mergeAll'

test('case 1', () => {
  const arr = [ { a : 1 }, { b : 2 }, { c : 3 } ]
  const expectedResult = {
    a : 1,
    b : 2,
    c : 3,
  }
  expect(mergeAll(arr)).toEqual(expectedResult)
})

test('case 2', () => {
  expect(mergeAll([ { foo : 1 }, { bar : 2 }, { baz : 3 } ])).toEqual({
    foo : 1,
    bar : 2,
    baz : 3,
  })
})

mergeDeepRight

mergeDeepRight<O1 extends object, O2 extends object>(x: O1, y: O2): Merge<O2, O1, 'deep'>

Creates a new object with the own properties of the first object merged with the own properties of the second object. If a key exists in both objects:

and both values are objects, the two values will be recursively merged
otherwise the value from the second object will be used.

All Typescript definitions

mergeDeepRight<O1 extends object, O2 extends object>(x: O1, y: O2): Merge<O2, O1, 'deep'>;
mergeDeepRight<O1 extends object>(x: O1): <O2 extends object>(y: O2) => Merge<O2, O1, 'deep'>;

R.mergeDeepRight source

import { type } from './type'

export function mergeDeepRight(target, source){
  if (arguments.length === 1){
    return sourceHolder => mergeDeepRight(target, sourceHolder)
  }

  const willReturn = JSON.parse(JSON.stringify(target))

  Object.keys(source).forEach(key => {
    if (type(source[ key ]) === 'Object'){
      if (type(target[ key ]) === 'Object'){
        willReturn[ key ] = mergeDeepRight(target[ key ], source[ key ])
      } else {
        willReturn[ key ] = source[ key ]
      }
    } else {
      willReturn[ key ] = source[ key ]
    }
  })

  return willReturn
}

Tests

// import { mergeDeepRight } from 'ramda'
import { mergeDeepRight } from './mergeDeepRight'

const slave = {
  name    : 'evilMe',
  age     : 10,
  contact : {
    a     : 1,
    email : 'foo@example.com',
  },
}
const master = {
  age     : 40,
  contact : { email : 'baz@example.com' },
  songs   : { title : 'Remains the same' },
}

test('happy', () => {
  const result = mergeDeepRight(slave, master)
  const curryResult = mergeDeepRight(slave)(master)
  const expected = {
    age     : 40,
    name    : 'evilMe',
    contact : {
      a     : 1,
      email : 'baz@example.com',
    },
    songs : { title : 'Remains the same' },
  }

  expect(result).toEqual(expected)
  expect(curryResult).toEqual(expected)
})

test('ramda compatible test 1', () => {
  const a = {
    w : 1,
    x : 2,
    y : { z : 3 },
  }
  const b = {
    a : 4,
    b : 5,
    c : { d : 6 },
  }
  const result = mergeDeepRight(a, b)
  const expected = {
    w : 1,
    x : 2,
    y : { z : 3 },
    a : 4,
    b : 5,
    c : { d : 6 },
  }

  expect(result).toEqual(expected)
})

test('ramda compatible test 2', () => {
  const a = {
    a : {
      b : 1,
      c : 2,
    },
    y : 0,
  }
  const b = {
    a : {
      b : 3,
      d : 4,
    },
    z : 0,
  }
  const result = mergeDeepRight(a, b)
  const expected = {
    a : {
      b : 3,
      c : 2,
      d : 4,
    },
    y : 0,
    z : 0,
  }

  expect(result).toEqual(expected)
})

test('ramda compatible test 3', () => {
  const a = {
    w : 1,
    x : { y : 2 },
  }
  const result = mergeDeepRight(a, { x : { y : 3 } })
  const expected = {
    w : 1,
    x : { y : 3 },
  }
  expect(result).toEqual(expected)
})

mergeRight

mergeRight(x: object, y: object): object

Same as R.merge, but in opposite direction.

const result = R.merge(
  {a:10},
  {a: 1, b: 2}
)
// => {a:10, b: 2}

Try the above R.mergeRight example in Rambda REPL

All Typescript definitions

mergeRight(x: object, y: object): object;
mergeRight(x: object): (y: object) => object;

R.mergeRight source

import { merge } from './merge'

export function mergeRight(x, y){
  return merge(y, x)
}

Tests

import { mergeRight } from './mergeRight'

test('', () => {
  const x = { a : 10 }
  const y = {
    a : 0,
    b : 1,
    c : 2,
  }
  const result = mergeRight(x, y)
  expect(result).toEqual({
    a : 10,
    b : 1,
    c : 2,
  })
})

min

min<T extends Ord>(x: T, y: T): T

It returns the lesser value between x and y.

const result = [
  R.min(5, 7),  
  R.min('bar', 'foo'),  
]
// => [5, 'bar']

Try the above R.min example in Rambda REPL

All Typescript definitions

min<T extends Ord>(x: T, y: T): T;
min<T extends Ord>(x: T): (y: T) => T;

R.min source

export function min(x, y){
  if (arguments.length === 1) return _y => min(x, _y)

  return y < x ? y : x
}

Tests

import { min } from './min'

test('happy', () => {
  expect(min(2, 1)).toBe(1)
  expect(min(2)(1)).toBe(1)
})

minBy

minBy<T>(compareFn: (input: T) => Ord, x: T, y: T): T

It returns the lesser value between x and y according to compareFn function.

const compareFn = Math.abs

R.minBy(compareFn, -5, 2) // => -5

Try the above R.minBy example in Rambda REPL

All Typescript definitions

minBy<T>(compareFn: (input: T) => Ord, x: T, y: T): T;
minBy<T>(compareFn: (input: T) => Ord, x: T): (y: T) => T;
minBy<T>(compareFn: (input: T) => Ord): FunctionToolbelt.Curry<(x: T, y: T) => T>;

R.minBy source

import { curry } from './curry'

export function minByFn(
  compareFn, x, y
){
  return compareFn(y) < compareFn(x) ? y : x
}

export const minBy = curry(minByFn)

Tests

import { minBy } from './minBy'

test('happy', () => {
  expect(minBy(
    Math.abs, -5, 2
  )).toEqual(2)
})

test('curried', () => {
  expect(minBy(Math.abs)(2, -5)).toEqual(2)
  expect(minBy(Math.abs)(2)(-5)).toEqual(2)
})

modulo

modulo(x: number, y: number): number

Curried version of x%y.

R.modulo(17, 3) // => 2

Try the above R.modulo example in Rambda REPL

All Typescript definitions

modulo(x: number, y: number): number;
modulo(x: number): (y: number) => number;

R.modulo source

export function modulo(x, y){
  if (arguments.length === 1) return _y => modulo(x, _y)

  return x % y
}

Tests

import { modulo } from './modulo'

test('happy', () => {
  expect(modulo(17, 3)).toEqual(2)
  expect(modulo(15)(6)).toEqual(3)
})

multiply

multiply(x: number, y: number): number

Curried version of x*y.

R.multiply(2, 4) // => 8

Try the above R.multiply example in Rambda REPL

All Typescript definitions

multiply(x: number, y: number): number;
multiply(x: number): (y: number) => number;

R.multiply source

export function multiply(x, y){
  if (arguments.length === 1) return _y => multiply(x, _y)

  return x * y
}

Tests

import { multiply } from './multiply'

test('happy', () => {
  expect(multiply(2, 4)).toEqual(8)
  expect(multiply(2)(4)).toEqual(8)
})

negate

negate(x: number): number

R.negate(420)// => -420

Try the above R.negate example in Rambda REPL

All Typescript definitions

negate(x: number): number;

R.negate source

export function negate(x){
  return -x
}

Tests

import { negate } from './negate'

test('negate', () => {
  expect(negate(420)).toEqual(-420)
  expect(negate(-13)).toEqual(13)
})

nextIndex

nextIndex(index: number, list: any[]): number

It returns the next index of the list.

If we have reached the end of the list, then it will return 0.

const list = [1, 2, 3]

const result = [
  R.nextIndex(0, list),
  R.nextIndex(1, list),
  R.nextIndex(2, list),
  R.nextIndex(10, list)
]
// => [1, 2, 0, 0]

Try the above R.nextIndex example in Rambda REPL

All Typescript definitions

nextIndex(index: number, list: any[]): number;

R.nextIndex source

export function nextIndex(index, list){
  return index >= list.length - 1 ? 0 : index + 1
}

Tests

import { nextIndex } from './nextIndex'

const list = [ 1, 2, 3, 4 ]

test('happy path', () => {
  expect(nextIndex(2, list)).toEqual(3)
})

test('go back to the start', () => {
  expect(nextIndex(3, list)).toEqual(0)
})

test('current index is too big', () => {
  expect(nextIndex(32, list)).toEqual(0)
})

test('with number as second input', () => {
  expect(nextIndex(3, 5)).toEqual(4)
  expect(nextIndex(4, 5)).toEqual(0)
})

none

none<T>(predicate: (x: T) => boolean, list: ReadonlyArray<T>): boolean

It returns true, if all members of array list returns false, when applied as argument to predicate function.

const list = [ 0, 1, 2, 3, 4 ]
const predicate = x => x > 6

const result = R.none(predicate, arr)
// => true

Try the above R.none example in Rambda REPL

All Typescript definitions

none<T>(predicate: (x: T) => boolean, list: ReadonlyArray<T>): boolean;
none<T>(predicate: (x: T) => boolean): (list: ReadonlyArray<T>) => boolean;

R.none source

export function none(predicate, list){
  if (arguments.length === 1) return _list => none(predicate, _list)

  return list.filter(predicate).length === 0
}

Tests

import { none } from './none'

const isEven = n => n % 2 === 0
const isOdd = n => n % 2 === 1
const arr = [ 1, 3, 5, 7, 9, 11 ]

test('when true', () => {
  expect(none(isEven, arr)).toBeTrue()
})

test('when false curried', () => {
  expect(none(isOdd)(arr)).toBeFalse()
})

test('passes index to predicate', () => {
  none((x, i) => {
    expect(typeof x).toBe('number')
    expect(typeof i).toBe('number')
  })([ 1, 2, 3 ])
})

not

not(input: any): boolean

It returns a boolean negated version of input.

R.not(false) // true

Try the above R.not example in Rambda REPL

All Typescript definitions

not(input: any): boolean;

R.not source

export function not(input){
  return !input
}

Tests

import { not } from './not'

test('not', () => {
  expect(not(false)).toEqual(true)
  expect(not(true)).toEqual(false)
  expect(not(0)).toEqual(true)
  expect(not(1)).toEqual(false)
})

nth

nth<T>(index: number, list: ReadonlyArray<T>): T | undefined

Curried version of list[index].

const list = [1, 2, 3]
const str = 'foo'

const result = [
  R.nth(2, list),
  R.nth(6, list),
  R.nth(0, str),
]
// => [3, undefined, 'f']

Try the above R.nth example in Rambda REPL

All Typescript definitions

nth<T>(index: number, list: ReadonlyArray<T>): T | undefined;
nth(index: number): <T>(list: ReadonlyArray<T>) => T | undefined;

R.nth source

export function nth(index, list){
  if (arguments.length === 1) return _list => nth(index, _list)

  const idx = index < 0 ? list.length + index : index

  return Object.prototype.toString.call(list) === '[object String]' ?
    list.charAt(idx) :
    list[ idx ]
}

Tests

import { nth } from './nth'

test('happy', () => {
  expect(nth(2, [ 1, 2, 3, 4 ])).toEqual(3)
})

test('with curry', () => {
  expect(nth(2)([ 1, 2, 3, 4 ])).toEqual(3)
})

test('with string', () => {
  expect(nth(2)('foo')).toEqual('o')
})

test('with negative index', () => {
  expect(nth(-3)([ 1, 2, 3, 4 ])).toEqual(2)
})

ok

ok(...inputs: any[]): (...schemas: any[]) => void | never

It checks if inputs are following schemas specifications according to R.isValid.

If validation fails, it throws.

const result = R.ok(
  1,
  ['foo', 'bar']
)(
  Number,
  [String]
)
// => undefined

Try the above R.ok example in Rambda REPL

All Typescript definitions

ok(...inputs: any[]): (...schemas: any[]) => void | never;

R.ok source

import { any } from './any'
import { glue } from './glue'
import { fromPrototypeToString, isValid } from './isValid'
import { map } from './map'
import { type } from './type'

export function schemaToString(schema){
  if (type(schema) !== 'Object'){
    return fromPrototypeToString(schema).rule
  }

  return map(x => {
    const { rule, parsed } = fromPrototypeToString(x)
    const xType = type(x)

    if (xType === 'Function' && !parsed) return 'Function'

    return parsed ? rule : xType
  }, schema)
}

export function check(singleInput, schema){
  return isValid({
    input  : { singleInput },
    schema : { singleInput : schema },
  })
}

export function ok(...inputs){
  return (...schemas) => {
    let failedSchema

    const anyError = any((singleInput, i) => {
      const schema = schemas[ i ] === undefined ? schemas[ 0 ] : schemas[ i ]

      const checked = check(singleInput, schema)
      if (!checked){
        failedSchema = JSON.stringify({
          input  : singleInput,
          schema : schemaToString(schema),
        })
      }

      return !checked
    }, inputs)

    if (anyError){
      const errorMessage =
        inputs.length > 1 ?
          glue(`
        Failed R.ok -
        reason: ${ failedSchema }
        all inputs: ${ JSON.stringify(inputs) }
        all schemas: ${ JSON.stringify(schemas.map(schemaToString)) }
      `,
          '\n') :
          `Failed R.ok - ${ failedSchema }`

      throw new Error(errorMessage)
    }

  }
}

Tests

import { ok, schemaToString } from './ok'

test('happy', () => {
  expect(() => {
    ok(
      1, 'foo', {}
    )(
      'number', 'string', 'object'
    )
  }).not.toThrow()
})

test('when validation fails', () => {
  expect(() => ok(
    1, 'foo', {}
  )(
    'number', 'string', 'string'
  )).toThrow()
})

/*
  TODO
  What about
  {a: Function}
*/
test('schema in error message', () => {
  const result = schemaToString({
    _a : [ Number ],
    a  : Number,
    b  : x => x > 2,
    c  : [ 'foo', 'bar' ],
    d  : [ { a : String } ],
    e  : 'boolean',
    f  : Array,
    h  : Object,
  })

  expect(JSON.stringify(result)).toMatchInlineSnapshot('"{\\"_a\\":\\"Array\\",\\"a\\":\\"number\\",\\"b\\":\\"Function\\",\\"c\\":\\"Array\\",\\"d\\":\\"Array\\",\\"e\\":\\"String\\",\\"f\\":\\"array\\",\\"h\\":\\"object\\"}"')
})

test('error contains schema', () => {
  try {
    ok(
      1, 'foo', {}
    )(
      { a : Number }, String, String
    )
    expect(false).toBe(true)
  } catch (e){
    expect(e.message.startsWith('Failed R.ok -')).toBeTruthy()
    expect(e).toBeInstanceOf(Error)
  }
})

test('when not throws with single schema', () => {
  expect(() => ok(
    1, 2, 3
  )('number')).not.toThrow()
})

test('when throws with single schema', () => {
  expect(() => ok(
    1, 2, '3'
  )('number')).toThrow()
})

omit

omit<T, K extends string>(propsToOmit: readonly K[], obj: T): Omit<T, K>

It returns a partial copy of an obj without propsToOmit properties.

const obj = {a: 1, b: 2, c: 3}
const propsToOmit = 'a,c,d'
const propsToOmitList = ['a', 'c', 'd']

const result = [
  R.omit(propsToOmit, obj), 
  R.omit(propsToOmitList, obj) 
]
// => [{b: 2}, {b: 2}]

Try the above R.omit example in Rambda REPL

All Typescript definitions

omit<T, K extends string>(propsToOmit: readonly K[], obj: T): Omit<T, K>;
omit<K extends string>(propsToOmit: readonly K[]): <T>(obj: T) => Omit<T, K>;
omit<T, U>(propsToOmit: string, obj: T): U;
omit<T, U>(propsToOmit: string): (obj: T) => U;
omit<T>(propsToOmit: string, obj: object): T;
omit<T>(propsToOmit: string): (obj: object) => T;

R.omit source

export function omit(propsToOmit, obj){
  if (arguments.length === 1) return _obj => omit(propsToOmit, _obj)

  if (obj === null || obj === undefined){
    return undefined
  }

  const propsToOmitValue =
    typeof propsToOmit === 'string' ? propsToOmit.split(',') : propsToOmit

  const willReturn = {}

  for (const key in obj){
    if (!propsToOmitValue.includes(key)){
      willReturn[ key ] = obj[ key ]
    }
  }

  return willReturn
}

Tests

import { omit } from './omit'

test('with string as condition', () => {
  const obj = {
    a : 1,
    b : 2,
    c : 3,
  }
  const result = omit('a,c', obj)
  const resultCurry = omit('a,c')(obj)
  const expectedResult = { b : 2 }

  expect(result).toEqual(expectedResult)
  expect(resultCurry).toEqual(expectedResult)
})

test('with null', () => {
  expect(omit('a,b', null)).toEqual(undefined)
})

test('doesn\'t work with number as property', () => {
  expect(omit([ 42 ], {
    a  : 1,
    42 : 2,
  })).toEqual({
    42 : 2,
    a  : 1,
  })
})

test('happy', () => {
  expect(omit([ 'a', 'c' ])({
    a : 'foo',
    b : 'bar',
    c : 'baz',
  })).toEqual({ b : 'bar' })
})

Typescript test

import {omit} from 'rambda'

describe('R.omit with array as props input', () => {
  it('allow Typescript to infer object type', () => {
    const input = {a: 'foo', b: 2, c: 3, d: 4}
    const result = omit(['b,c'], input)

    result.a // $ExpectType string
    result.d // $ExpectType number

    const curriedResult = omit(['a,c'], input)

    curriedResult.a // $ExpectType string
    curriedResult.d // $ExpectType number
  })

  it('declare type of input object', () => {
    interface Input {
      a: string,
      b: number,
      c: number,
      d: number,
    }
    const input: Input = {a: 'foo', b: 2, c: 3, d: 4}
    const result = omit(['b,c'], input)
    result // $ExpectType Pick<Input, "a" | "b" | "c" | "d">

    result.a // $ExpectType string
    result.d // $ExpectType number

    const curriedResult = omit(['a,c'], input)

    curriedResult.a // $ExpectType string
    curriedResult.d // $ExpectType number
  })
})

describe('R.omit with string as props input', () => {
  interface Output {
    b: number,
    d: number,
  }

  it('explicitly declare output', () => {
    const result = omit<Output>('a,c', {a: 1, b: 2, c: 3, d: 4})
    result // $ExpectType Output
    result.b // $ExpectType number

    const curriedResult = omit<Output>('a,c')({a: 1, b: 2, c: 3, d: 4})

    curriedResult.b // $ExpectType number
  })

  it('explicitly declare input and output', () => {
    interface Input {
      a: number,
      b: number,
      c: number,
      d: number,
    }
    const result = omit<Input, Output>('a,c', {a: 1, b: 2, c: 3, d: 4})
    result // $ExpectType Output
    result.b // $ExpectType number

    const curriedResult = omit<Input, Output>('a,c')({
      a: 1,
      b: 2,
      c: 3,
      d: 4,
    })

    curriedResult.b // $ExpectType number
  })

  it('without passing type', () => {
    const result = omit('a,c', {a: 1, b: 2, c: 3, d: 4})
    result // $ExpectType unknown
  })
})

once

once(fn: Func<any>): Func<any>

It returns a function, which invokes only once fn function.

let result = 0
const addOnce = R.once((x) => result = result + x)

addOnce(1)
addOnce(1)
// => 1

Try the above R.once example in Rambda REPL

All Typescript definitions

once(fn: Func<any>): Func<any>;

R.once source

import { curry } from './curry'

function onceFn(fn, context){
  let result

  return function (){
    if (fn){
      result = fn.apply(context || this, arguments)
      fn = null
    }

    return result
  }
}

export function once(fn, context){
  if (arguments.length === 1){
    const wrap = onceFn(fn, context)

    return curry(wrap)
  }

  return onceFn(fn, context)
}

Tests

import { once } from './once'

test('with counter', () => {
  let counter = 0
  const runOnce = once(x => {
    counter++

    return x + 2
  })
  expect(runOnce(1)).toEqual(3)
  runOnce(1)
  runOnce(1)
  runOnce(1)
  expect(counter).toEqual(1)
})

test('happy path', () => {
  const addOneOnce = once((
    a, b, c
  ) => a + b + c, 1)

  expect(addOneOnce(
    10, 20, 30
  )).toBe(60)
  expect(addOneOnce(40)).toEqual(60)
})

over

over<T>(lens: Lens, fn: Arity1Fn, value: T): T

It returns a copied Object or Array with modified value received by applying function fn to lens focus.

const headLens = R.lensIndex(0)
 
R.over(headLens, R.toUpper, ['foo', 'bar', 'baz']) //=> ['FOO', 'bar', 'baz']

Try the above R.over example in Rambda REPL

All Typescript definitions

over<T>(lens: Lens, fn: Arity1Fn, value: T): T;
over<T>(lens: Lens, fn: Arity1Fn, value: readonly T[]): T[];
over(lens: Lens, fn: Arity1Fn): <T>(value: T) => T;
over(lens: Lens, fn: Arity1Fn): <T>(value: readonly T[]) => T[];
over(lens: Lens): <T>(fn: Arity1Fn, value: T) => T;
over(lens: Lens): <T>(fn: Arity1Fn, value: readonly T[]) => T[];

R.over source

const Identity = x => ({
  x,
  map : fn => Identity(fn(x)),
})

export function over(
  lens, fn, object
){
  if (arguments.length === 1)
    return (_fn, _object) => over(
      lens, _fn, _object
    )
  if (arguments.length === 2) return _object => over(
    lens, fn, _object
  )

  return lens(x => Identity(fn(x)))(object).x
}

partial

partial<V0, V1, T>(fn: (x0: V0, x1: V1) => T, x0: V0): (x1: V1) => T

It is very similar to R.curry, but you can pass initial arguments when you create the curried function.

R.partial will keep returning a function until all the arguments that the function fn expects are passed. The name comes from the fact that you partially inject the inputs.

const fn = (title, firstName, lastName) => {
  return title + ' ' + firstName + ' ' + lastName + '!'
}

const canPassAnyNumberOfArguments = R.partial(fn, 'Hello')
const ramdaStyle = R.partial(fn, ['Hello'])

const finalFn = canPassAnyNumberOfArguments('Foo')

finalFn('Bar') // =>  'Hello, Foo Bar!'

Try the above R.partial example in Rambda REPL

All Typescript definitions

partial<V0, V1, T>(fn: (x0: V0, x1: V1) => T, x0: V0): (x1: V1) => T;
partial<V0, V1, V2, T>(fn: (x0: V0, x1: V1, x2: V2) => T, x0: V0, x1: V1): (x2: V2) => T;
partial<V0, V1, V2, T>(fn: (x0: V0, x1: V1, x2: V2) => T, x0: V0): (x1: V1, x2: V2) => T;
partial<V0, V1, V2, V3, T>(fn: (x0: V0, x1: V1, x2: V2, x3: V3) => T, x0: V0, x1: V1, x2: V2): (x2: V3) => T;
partial<V0, V1, V2, V3, T>(fn: (x0: V0, x1: V1, x2: V2, x3: V3) => T, x0: V0, x1: V1): (x2: V2, x3: V3) => T;
partial<V0, V1, V2, V3, T>(fn: (x0: V0, x1: V1, x2: V2, x3: V3) => T, x0: V0): (x1: V1, x2: V2, x3: V3) => T;
partial<T>(fn: (...a: any[]) => T, ...args: any[]): (...a: any[]) => T;

R.partial source

export function partial(fn, ...args){
  const len = fn.length

  return (...rest) => {
    if (args.length + rest.length >= len){
      return fn(...args, ...rest)
    }

    return partial(fn, ...[ ...args, ...rest ])
  }
}

Tests

import { partial } from './partial'
import { type } from './type'

const greet = (
  salutation, title, firstName, lastName
) =>
  salutation + ', ' + title + ' ' + firstName + ' ' + lastName + '!'

test('happy', () => {
  const canPassAnyNumberOfArguments = partial(
    greet, 'Hello', 'Ms.'
  )
  const fn = canPassAnyNumberOfArguments('foo')
  const sayHello = partial(greet, [ 'Hello' ])
  const sayHelloRamda = partial(sayHello, [ 'Ms.' ])

  expect(type(fn)).toBe('Function')

  expect(fn('bar')).toBe('Hello, Ms. foo bar!')
  expect(sayHelloRamda('foo', 'bar')).toBe('Hello, Ms. foo bar!')
})

test('extra arguments are ignored', () => {
  const canPassAnyNumberOfArguments = partial(
    greet, 'Hello', 'Ms.'
  )
  const fn = canPassAnyNumberOfArguments('foo')

  expect(type(fn)).toBe('Function')

  expect(fn(
    'bar', 1, 2
  )).toBe('Hello, Ms. foo bar!')
})

test('when array is input', () => {
  const fooFn = (
    a, b, c, d
  ) => ({
    a,
    b,
    c,
    d,
  })
  const barFn = partial(
    fooFn, [ 1, 2 ], []
  )

  expect(barFn(1, 2)).toEqual({
    a : [ 1, 2 ],
    b : [],
    c : 1,
    d : 2,
  })
})

test('ramda spec', () => {
  const sayHello = partial(greet, 'Hello')
  const sayHelloToMs = partial(sayHello, 'Ms.')

  expect(sayHelloToMs('Jane', 'Jones')).toBe('Hello, Ms. Jane Jones!')
})

partition

partition<T>(
  predicate: Predicatex<T>,
  input: T[]
): [T[], T[]]

It will return array of two objects/arrays according to predicate function. The first member holds all instanses of input that pass the predicate function, while the second member - those who doesn't.

input can be either an object or an array.

const list = [1, 2, 3]
const obj = {a: 1, b: 2, c: 3}
const predicate = x => x > 2

const result = [
  R.partition(predicate, list),
  R.partition(predicate, obj)
]
const expected = [
  [[3], [1, 2]],
  [{c: 3},  {a: 1, b: 2}],
]
// `result` is equal to `expected`

Try the above R.partition example in Rambda REPL

All Typescript definitions

partition<T>(
  predicate: Predicatex<T>,
  input: T[]
): [T[], T[]];
partition<T>(
  predicate: Predicatex<T>
): (input: T[]) => [T[], T[]];

R.partition source

import { _isArray } from './_internals/_isArray'

function whenObject(predicate, input){
  const yes = {}
  const no = {}
  Object.entries(input).forEach(([ prop, value ]) => {
    if (predicate(value, prop)){
      yes[ prop ] = value
    } else {
      no[ prop ] = value
    }
  })

  return [ yes, no ]
}

export function partition(predicate, input){
  if (arguments.length === 1){
    return listHolder => partition(predicate, listHolder)
  }
  if (!_isArray(input)) return whenObject(predicate, input)

  const yes = []
  const no = []
  let counter = -1

  while (counter++ < input.length - 1){
    if (predicate(input[ counter ], counter)){
      yes.push(input[ counter ])
    } else {
      no.push(input[ counter ])
    }
  }

  return [ yes, no ]
}

Tests

import { partition } from './partition'

test('with array', () => {
  const predicate = (x, i) => {
    expect(typeof i).toBe('number')

    return x > 2
  }
  const list = [ 1, 2, 3, 4 ]

  const result = partition(predicate, list)
  const expectedResult = [
    [ 3, 4 ],
    [ 1, 2 ],
  ]

  expect(result).toEqual(expectedResult)
})

test('with object', () => {
  const predicate = (value, prop) => {
    expect(typeof prop).toBe('string')

    return value > 2
  }
  const hash = {
    a : 1,
    b : 2,
    c : 3,
    d : 4,
  }

  const result = partition(predicate)(hash)
  const expectedResult = [
    {
      c : 3,
      d : 4,
    },
    {
      a : 1,
      b : 2,
    },
  ]

  expect(result).toEqual(expectedResult)
})

test('readme example', () => {
  const list = [ 1, 2, 3 ]
  const obj = {
    a : 1,
    b : 2,
    c : 3,
  }
  const predicate = x => x > 2

  const result = [ partition(predicate, list), partition(predicate, obj) ]
  const expected = [
    [ [ 3 ], [ 1, 2 ] ],
    [ { c : 3 }, {
      a : 1,
      b : 2,
    } ],
  ]
  expect(result).toEqual(expected)
})

pass

pass(...inputs: any[]): (...rules: any[]) => boolean

It checks if inputs are following schemas specifications according to R.isValid.

const result = R.pass(
  1,
  ['foo','bar']
)(
  Number,
  [String]
)
// => true

Try the above R.pass example in Rambda REPL

All Typescript definitions

pass(...inputs: any[]): (...rules: any[]) => boolean;

R.pass source

import { any } from './any'
import { check } from './ok'

export function pass(...inputs){
  return (...schemas) =>
    any((x, i) => {
      const schema = schemas[ i ] === undefined ? schemas[ 0 ] : schemas[ i ]

      return !check(x, schema)
    }, inputs) === false
}

Tests

import { pass } from './pass'

test('true on success', () => {
  const result = pass(
    1, 'foo', {}
  )(
    'number', 'string', 'object'
  )

  expect(result).toBe(true)
})

test('false on failure', () => {
  expect(pass(
    1, 'foo', {}
  )(
    'number', 'string', 'string'
  )).toBe(false)
})

test('true when single schema', () => {
  expect(pass(
    1, 2, 3
  )('number')).toBe(true)
})

test('false when single schema', () => {
  expect(pass(
    1, 'foo', {}
  )('number')).toBe(false)
})

test('array of schemas', () => {
  const result = pass([ { a : 1 }, { a : 2 }, { a : 3 } ])([ { a : Number } ])
  expect(result).toBeTruthy()
})

test('reame example', () => {
  const result = pass(1, [ 'foo', 'bar' ])(Number, [ String ])
  expect(result).toBeTruthy()
})

path

path<Input, T>(pathToSearch: string | string[], obj: Input): T | undefined

If pathToSearch is 'a.b' then it will return 1 if obj is {a:{b:1}}.

It will return undefined, if such path is not found.

const obj = {a: {b: 1}}
const pathToSearch = 'a.b'
const pathToSearchList = ['a', 'b']

const result = [
  R.path(pathToSearch, obj),
  R.path(pathToSearchList, obj),
  R.path('a.b.c.d', obj)
]
// => [1, 1, undefined]

Try the above R.path example in Rambda REPL

All Typescript definitions

path<Input, T>(pathToSearch: string | string[], obj: Input): T | undefined;
path<T>(pathToSearch: string | string[], obj: any): T | undefined;
path<T>(pathToSearch: string | string[]): (obj: any) => T | undefined;
path<Input, T>(pathToSearch: string | string[]): (obj: Input) => T | undefined;

R.path source

export function path(list, obj){
  if (arguments.length === 1) return _obj => path(list, _obj)

  if (obj === null || obj === undefined){
    return undefined
  }
  let willReturn = obj
  let counter = 0

  const pathArrValue = typeof list === 'string' ? list.split('.') : list

  while (counter < pathArrValue.length){
    if (willReturn === null || willReturn === undefined){
      return undefined
    }
    willReturn = willReturn[ pathArrValue[ counter ] ]
    counter++
  }

  return willReturn
}

Tests

import { path } from './path'

test('with array inside object', () => {
  const obj = { a : { b : [ 1, { c : 1 } ] } }

  expect(path('a.b.1.c', obj)).toBe(1)
})

test('works with undefined', () => {
  const obj = { a : { b : { c : 1 } } }

  expect(path('a.b.c.d.f', obj)).toBeUndefined()
  expect(path('foo.babaz', undefined)).toBeUndefined()
  expect(path('foo.babaz')(undefined)).toBeUndefined()
})

test('works with string instead of array', () => {
  expect(path('foo.bar.baz')({ foo : { bar : { baz : 'yes' } } })).toEqual('yes')
})

test('path', () => {
  expect(path([ 'foo', 'bar', 'baz' ])({ foo : { bar : { baz : 'yes' } } })).toEqual('yes')

  expect(path([ 'foo', 'bar', 'baz' ])(null)).toBeUndefined()

  expect(path([ 'foo', 'bar', 'baz' ])({ foo : { bar : 'baz' } })).toBeUndefined()
})

Typescript test

import {path} from 'rambda'

interface Input {
  a: number,
  b: {
    c: boolean,
  },
}

describe('path', () => {
  it('without specified input type', () => {
    const input = {a: 1, b: {c: true}}
    const result = path<boolean>('a.b.c', input)
    const resultCurried = path<boolean>('a.b.c')(input)
    result // $ExpectType boolean | undefined
    resultCurried // $ExpectType boolean | undefined
  })

  it('without specified output type', () => {
    const input = {a: 1, b: {c: true}}
    const result = path('a.b.c', input)
    result // $ExpectType unknown
  })

  it('with string as path', () => {
    const input: Input = {a: 1, b: {c: true}}
    const resultA = path<boolean>('a.b.c', input)
    const resultB = path<boolean>('a.b.c')(input)
    resultA // $ExpectType boolean | undefined
    resultB // $ExpectType boolean | undefined
  })
  it('with array as path', () => {
    const input: Input = {a: 1, b: {c: true}}
    const resultA = path<boolean>(['a', 'b', 'c'], input)
    const resultB = path<boolean>(['a', 'b', 'c'])(input)
    resultA // $ExpectType boolean | undefined
    resultB // $ExpectType boolean | undefined
  })
})

describe('path with specified input', () => {
  it('with string as path', () => {
    const input: Input = {a: 1, b: {c: true}}
    // const wrongInput = { a: 1, b: true }
    // const resultA = path<Input, boolean>('a.b.c', wrongInput)
    const resultA = path<Input, boolean>('a.b.c', input)
    const resultB = path<Input, boolean>('a.b.c')(input)
    resultA // $ExpectType boolean | undefined
    resultB // $ExpectType boolean | undefined
  })
  it('with array as path', () => {
    const input: Input = {a: 1, b: {c: true}}
    const resultA = path<Input, boolean>(['a', 'b', 'c'], input)
    const resultB = path<Input, boolean>(['a', 'b', 'c'])(input)
    resultA // $ExpectType boolean | undefined
    resultB // $ExpectType boolean | undefined
  })
})

1 failed Ramda.path specs

💥 Reason for the failure: ramda method supports negative indices

var R = require('../../../../dist/rambda.js');
var eq = require('./shared/eq');

describe('path', function() {
  var deepObject = {a: {b: {c: 'c'}}, falseVal: false, nullVal: null, undefinedVal: undefined, arrayVal: ['arr']};
  it('takes a path that contains negative indices into arrays', function() {
    eq(R.path(['x', -2], {x: ['a', 'b', 'c', 'd']}), 'c');
    eq(R.path([-1, 'y'], [{x: 1, y: 99}, {x: 2, y: 98}, {x: 3, y: 97}]), 97);
  });
});

pathEq

pathEq(path: string | string[], target: any, input: object): boolean

const path = 'a.b'
const target = 1
const input = {a: {b:1}}

const result = R.pathEq(
  path,
  target,
  input
)
// => true

Try the above R.pathEq example in Rambda REPL

All Typescript definitions

pathEq(path: string | string[], target: any, input: object): boolean;
pathEq(path: string | string[], target: any): (input: object) => boolean;

R.pathEq source

import { path as pathModule } from './path'

export function pathEq(
  path, target, obj
){
  if (arguments.length === 2){
    return objHolder => pathEq(
      path, target, objHolder
    )
  }

  return pathModule(path, obj) === target
}

Tests

import { pathEq } from './pathEq'

test('when true', () => {
  const path = 'a.b'
  const obj = { a : { b : 1 } }
  const target = 1

  expect(pathEq(
    path, target, obj
  )).toBe(true)
})

test('when false', () => {
  const path = 'a.b'
  const obj = { a : { b : 1 } }
  const target = 2

  expect(pathEq(path, target)(obj)).toBe(false)
})

test('when wrong path', () => {
  const path = 'foo.bar'
  const obj = { a : { b : 1 } }
  const target = 2

  expect(pathEq(
    path, target, obj
  )).toBe(false)
})

pathOr

pathOr<T>(defaultValue: T, pathToSearch: Path, obj: any): T

It reads obj input and returns either R.path(pathToSearch, obj) result or defaultValue input.

const defaultValue = 'DEFAULT_VALUE'
const pathToSearch = 'a.b'
const pathToSearchList = ['a', 'b']

const obj = {
  a : {
    b : 1
  }
}

const result = [
  R.pathOr(DEFAULT_VALUE, pathToSearch, obj) 
  R.pathOr(DEFAULT_VALUE, pathToSearchList, obj) 
  R.pathOr(DEFAULT_VALUE, 'a.b.c', obj) 
]
// => [1, 1, 'DEFAULT_VALUE']

Try the above R.pathOr example in Rambda REPL

All Typescript definitions

pathOr<T>(defaultValue: T, pathToSearch: Path, obj: any): T;
pathOr<T>(defaultValue: T, pathToSearch: Path): (obj: any) => T;
pathOr<T>(defaultValue: T): FunctionToolbelt.Curry<(a: Path, b: any) => T>;

R.pathOr source

import { curry } from './curry'
import { defaultTo } from './defaultTo'
import { path } from './path'

function pathOrFn(
  defaultValue, list, obj
){
  return defaultTo(defaultValue, path(list, obj))
}

export const pathOr = curry(pathOrFn)

Tests

import { pathOr } from './pathOr'

test('with undefined', () => {
  const result = pathOr(
    'foo', 'x.y', { x : { y : 1 } }
  )

  expect(result).toEqual(1)
})

test('with null', () => {
  const result = pathOr(
    'foo', 'x.y', null
  )

  expect(result).toEqual('foo')
})

test('with NaN', () => {
  const result = pathOr(
    'foo', 'x.y', NaN
  )

  expect(result).toEqual('foo')
})

test('curry case (x)(y)(z)', () => {
  const result = pathOr('foo')('x.y.z')({ x : { y : { a : 1 } } })

  expect(result).toEqual('foo')
})

test('curry case (x)(y,z)', () => {
  const result = pathOr('foo', 'x.y.z')({ x : { y : { a : 1 } } })

  expect(result).toEqual('foo')
})

test('curry case (x,y)(z)', () => {
  const result = pathOr('foo')('x.y.z', { x : { y : { a : 1 } } })

  expect(result).toEqual('foo')
})

paths

paths<Input, T>(pathsToSearch: Path[], obj: Input): (T | undefined)[]

It loops over members of pathsToSearch as singlePath and returns the array produced by R.path(singlePath, obj).

Because it calls R.path, then singlePath can be either string or a list.

const obj = {
  a : {
    b : {
      c : 1,
      d : 2
    }
  }
}

const result = R.paths([
  'a.b.c',
  'a.b.c.d',
  'a.b.c.d.e',
], obj)
// => [1, 2, undefined]

Try the above R.paths example in Rambda REPL

All Typescript definitions

paths<Input, T>(pathsToSearch: Path[], obj: Input): (T | undefined)[];
paths<Input, T>(pathsToSearch: Path[]): (obj: Input) => (T | undefined)[];
paths<T>(pathsToSearch: Path[], obj: any): (T | undefined)[];
paths<T>(pathsToSearch: Path[]): (obj: any) => (T | undefined)[];

R.paths source

import { path } from './path'

export function paths(pathsToSearch, obj){
  if (arguments.length === 1){
    return _obj => paths(pathsToSearch, _obj)
  }

  return pathsToSearch.map(singlePath => path(singlePath, obj))
}

Tests

import { paths } from './paths'

const obj = {
  a : {
    b : {
      c : 1,
      d : 2,
    },
  },
  p : [ { q : 3 }, 'Hi' ],
  x : {
    y : 'Alice',
    z : [ [ {} ] ],
  },
}

test('with string path + curry', () => {
  const pathsInput = [ 'a.b.d', 'p.q' ]
  const expected = [ 2, undefined ]
  const result = paths(pathsInput, obj)
  const curriedResult = paths(pathsInput)(obj)

  expect(result).toEqual(expected)
  expect(curriedResult).toEqual(expected)
})

test('with array path', () => {
  const result = paths([
    [ 'a', 'b', 'c' ],
    [ 'x', 'y' ],
  ],
  obj)

  expect(result).toEqual([ 1, 'Alice' ])
})

test('takes a paths that contains indices into arrays', () => {
  expect(paths([
    [ 'p', 0, 'q' ],
    [ 'x', 'z', 0, 0 ],
  ],
  obj)).toEqual([ 3, {} ])
  expect(paths([
    [ 'p', 0, 'q' ],
    [ 'x', 'z', 2, 1 ],
  ],
  obj)).toEqual([ 3, undefined ])
})

test('gets a deep property\'s value from objects', () => {
  expect(paths([ [ 'a', 'b' ] ], obj)).toEqual([ obj.a.b ])
  expect(paths([ [ 'p', 0 ] ], obj)).toEqual([ obj.p[ 0 ] ])
})

test('returns undefined for items not found', () => {
  expect(paths([ [ 'a', 'x', 'y' ] ], obj)).toEqual([ undefined ])
  expect(paths([ [ 'p', 2 ] ], obj)).toEqual([ undefined ])
})

Typescript test

import {paths} from 'rambda'

interface Input {
  a: number,
  b: number,
  c: number,
}

const input: Input = {a: 1, b: 2, c: 3}

describe('paths', () => {
  it('with dot notation', () => {
    const result = paths<number>(['a.b.c', 'foo.bar'], input)
    result // $ExpectType (number | undefined)[]
  })

  it('without type', () => {
    const result = paths(['a.b.c', 'foo.bar'], input)
    result // $ExpectType unknown[]
  })

  it('with array as path', () => {
    const result = paths<number>([['a', 'b', 'c'], ['foo.bar']], input)
    result // $ExpectType (number | undefined)[]
  })

  it('with curry', () => {
    const result = paths<number>([['a', 'b', 'c'], ['foo.bar']])(input)
    result // $ExpectType (number | undefined)[]
  })
})

1 failed Ramda.paths specs

💥 Reason for the failure: ramda method supports negative indices

var R = require('../../../../dist/rambda.js');
var eq = require('./shared/eq');

describe('paths', function() {
  var obj = {
    a: {
      b: {
        c: 1,
        d: 2
      }
    },
    p: [{q: 3}, 'Hi'],
    x: {
      y: 'Alice',
      z: [[{}]]
    }
  };
  it('takes a path that contains negative indices into arrays', function() {
    eq(R.paths([['p', -2, 'q'], ['p', -1]], obj), [3, 'Hi']);
    eq(R.paths([['p', -4, 'q'], ['x', 'z', -1, 0]], obj), [undefined, {}]);
  });
});

pick

pick<T, K extends string | number | symbol>(propsToPick: readonly K[], input: T): Pick<T, Exclude<keyof T, Exclude<keyof T, K>>>

It returns a partial copy of an input containing only propsToPick properties.

input can be either an object or an array.

String anotation of propsToPick is one of the differences between Rambda and Ramda.

const obj = {
  a : 1,
  b : false,
  foo: 'cherry'
}
const list = [1, 2, 3, 4]
const propsToPick = 'a,foo'
const propsToPickList = ['a', 'foo']

const result = [
  R.pick(propsToPick, obj),
  R.pick(propsToPickList, obj),
  R.pick('a,bar', obj),
  R.pick('bar', obj),
  R.pick([0, 3], list),
  R.pick('0,3', list),
]

const expected = [
  {a:1, foo: 'cherry'},
  {a:1, foo: 'cherry'},
  {a:1},
  {},
  [1,4],
  [1,4]
]
// => `result` is equal to `expected`

Try the above R.pick example in Rambda REPL

All Typescript definitions

pick<T, K extends string | number | symbol>(propsToPick: readonly K[], input: T): Pick<T, Exclude<keyof T, Exclude<keyof T, K>>>;
pick<K extends string | number | symbol>(propsToPick: readonly K[]): <T>(input: T) => Pick<T, Exclude<keyof T, Exclude<keyof T, K>>>;
pick<T, U>(propsToPick: string, input: T): U;
pick<T, U>(propsToPick: string): (input: T) => U;
pick<T>(propsToPick: string, input: object): T;
pick<T>(propsToPick: string): (input: object) => T;

R.pick source

export function pick(propsToPick, input){
  if (arguments.length === 1) return _input => pick(propsToPick, _input)

  if (input === null || input === undefined){
    return undefined
  }
  const keys =
    typeof propsToPick === 'string' ? propsToPick.split(',') : propsToPick

  const willReturn = {}
  let counter = 0

  while (counter < keys.length){
    if (keys[ counter ] in input){
      willReturn[ keys[ counter ] ] = input[ keys[ counter ] ]
    }
    counter++
  }

  return willReturn
}

Tests

import { pick } from './pick'

test('props to pick is a string', () => {
  const obj = {
    a : 1,
    b : 2,
    c : 3,
  }
  const result = pick('a,c', obj)
  const resultCurry = pick('a,c')(obj)
  const expectedResult = {
    a : 1,
    c : 3,
  }

  expect(result).toEqual(expectedResult)
  expect(resultCurry).toEqual(expectedResult)
})

test('props to pick is an array', () => {
  expect(pick([ 'a', 'c' ])({
    a : 'foo',
    b : 'bar',
    c : 'baz',
  })).toEqual({
    a : 'foo',
    c : 'baz',
  })

  expect(pick([ 'a', 'd', 'e', 'f' ])({
    a : 'foo',
    b : 'bar',
    c : 'baz',
  })).toEqual({ a : 'foo' })

  expect(pick('a,d,e,f')(null)).toEqual(undefined)
})

test('works with list as input and number as props - props to pick is an array', () => {
  const result = pick([ 1, 2 ], [ 'a', 'b', 'c', 'd' ])
  expect(result).toEqual({
    1 : 'b',
    2 : 'c',
  })
})

test('works with list as input and number as props - props to pick is a string', () => {
  const result = pick('1,2', [ 'a', 'b', 'c', 'd' ])
  expect(result).toEqual({
    1 : 'b',
    2 : 'c',
  })
})

test('with symbol', () => {
  const symbolProp = Symbol('s')
  expect(pick([ symbolProp ], { [ symbolProp ] : 'a' })).toMatchInlineSnapshot(`
    Object {
      Symbol(s): "a",
    }
  `)
})

Typescript test

import {pick} from 'rambda'

describe('pick with array as props input', () => {
  interface Input {
    a: string,
    b: number,
    c: number,
    d: number,
  }

  it('need to declare the types of input and props to pick - string as prop', () => {
    const input = {a: 'foo', b: 2, c: 3, d: 4}
    const result = pick<Input, string>(['a,c'], input)
    result // $ExpectType Pick<Input, "a" | "b" | "c" | "d">
    result.a // $ExpectType string
    result.b // $ExpectType number

    const curriedResult = pick<Input, string>(['a,c'], input)
    curriedResult // $ExpectType Pick<Input, "a" | "b" | "c" | "d">
  })

  it('need to declare the types of input and props to pick - number as prop', () => {
    const result = pick<string[], number>([1, 2], ['a', 'b', 'c', 'd'])
    result[1] // $ExpectType string
    result[2] // $ExpectType string
    result[3] // should not be possible but it is
  })

  it('need to declare the types of input and props to pick - symbol as prop', () => {
    const symbolProp = Symbol('s')
    const result = pick([symbolProp], {[symbolProp]: 'a'})

    result // $ExpectType Pick<{ [symbolProp]: string; }, typeof symbolProp>
  })
})

describe('R.pick with string as props input', () => {
  interface Output {
    a: number,
    c: number,
  }

  it('explicitly declare output', () => {
    const result = pick<Output>('a,c', {a: 1, b: 2, c: 3, d: 4})
    result // $ExpectType Output
    result.a // $ExpectType number

    const curriedResult = pick<Output>('a,c')({a: 1, b: 2, c: 3, d: 4})

    curriedResult.a // $ExpectType number
  })

  it('explicitly declare input and output', () => {
    interface Input {
      a: number,
      b: number,
      c: number,
      d: number,
    }
    const result = pick<Input, Output>('a,c', {a: 1, b: 2, c: 3, d: 4})
    result // $ExpectType Output
    result.a // $ExpectType number

    const curriedResult = pick<Input, Output>('a,c')({
      a: 1,
      b: 2,
      c: 3,
      d: 4,
    })

    curriedResult.a // $ExpectType number
  })

  it('without passing type', () => {
    const result = pick('a,c', {a: 1, b: 2, c: 3, d: 4})
    result // $ExpectType unknown
  })
})

pickAll

pickAll<T, U>(propsToPick: ReadonlyArray<string>, obj: T): U

Same as R.pick but it won't skip the missing props, i.e. it will assign them to undefined.

const obj = {
  a : 1,
  b : false,
  foo: 'cherry'
}
const propsToPick = 'a,foo,bar'
const propsToPickList = ['a', 'foo', 'bar']

const result = [
  R.pickAll(propsToPick, obj),
  R.pickAll(propsToPickList, obj),
  R.pickAll('a,bar', obj),
  R.pickAll('bar', obj),
]
const expected = [
  {a:1, foo: 'cherry', bar: undefined},
  {a:1, foo: 'cherry', bar: undefined},
  {a:1, bar: undefined},
  {bar: undefined}
]
// => `result` is equal to `expected`

Try the above R.pickAll example in Rambda REPL

All Typescript definitions

pickAll<T, U>(propsToPick: ReadonlyArray<string>, obj: T): U;
pickAll(propsToPick: ReadonlyArray<string>): <T, U>(obj: T) => U;

R.pickAll source

export function pickAll(propsToPick, obj){
  if (arguments.length === 1) return _obj => pickAll(propsToPick, _obj)

  if (obj === null || obj === undefined){
    return undefined
  }
  const keysValue =
    typeof propsToPick === 'string' ? propsToPick.split(',') : propsToPick

  const willReturn = {}
  let counter = 0

  while (counter < keysValue.length){
    if (keysValue[ counter ] in obj){
      willReturn[ keysValue[ counter ] ] = obj[ keysValue[ counter ] ]
    } else {
      willReturn[ keysValue[ counter ] ] = undefined
    }
    counter++
  }

  return willReturn
}

Tests

import { pickAll } from './pickAll'

test('when input is undefined or null', () => {
  expect(pickAll('a', null)).toBe(undefined)
  expect(pickAll('a', undefined)).toBe(undefined)
})

test('with string as condition', () => {
  const obj = {
    a : 1,
    b : 2,
    c : 3,
  }
  const result = pickAll('a,c', obj)
  const resultCurry = pickAll('a,c')(obj)
  const expectedResult = {
    a : 1,
    b : undefined,
    c : 3,
  }

  expect(result).toEqual(expectedResult)
  expect(resultCurry).toEqual(expectedResult)
})

test('with array as condition', () => {
  expect(pickAll([ 'a', 'b', 'c' ], {
    a : 'foo',
    c : 'baz',
  })).toEqual({
    a : 'foo',
    b : undefined,
    c : 'baz',
  })
})

pipe

pipe<T1>(fn0: () => T1): () => T1

It performs left-to-right function composition.

const result = R.pipe(
  R.filter(val => val > 2),
  R.map(a => a * 2)
)([1, 2, 3, 4])

// => [6, 8]

Try the above R.pipe example in Rambda REPL

All Typescript definitions

pipe<T1>(fn0: () => T1): () => T1;
pipe<V0, T1>(fn0: (x0: V0) => T1): (x0: V0) => T1;
pipe<V0, V1, T1>(fn0: (x0: V0, x1: V1) => T1): (x0: V0, x1: V1) => T1;
pipe<V0, V1, V2, T1>(fn0: (x0: V0, x1: V1, x2: V2) => T1): (x0: V0, x1: V1, x2: V2) => T1;

R.pipe source

import { compose } from './compose'

export function pipe(...fns){
  if (fns.length === 0)
    throw new Error('pipe requires at least one argument')

  return compose(...fns.reverse())
}

Tests

import { add, last, map } from '../rambda'
import { pipe } from './pipe'

test('happy', () => {
  const list = [ 1, 2, 3 ]

  const result = pipe(
    map(add(1)), map(add(10)), last
  )(list)

  expect(result).toEqual(14)
})

test('with bad input', () => {
  expect(() => pipe()).toThrow('pipe requires at least one argument')
})

3 failed Ramda.pipe specs

💥 Reason for the failure: ramda passes context to functions | rambda composed functions have no length

var assert = require('assert');

var R = require('../../../../dist/rambda.js');
var eq = require('./shared/eq');
describe('pipe', function() {
  it('performs left-to-right function composition', function() {
    //  f :: (String, Number?) -> ([Number] -> [Number])
    var f = R.pipe(parseInt, R.multiply, R.map);
    eq(f.length, 2);
    eq(f('10')([1, 2, 3]), [10, 20, 30]);
    eq(f('10', 2)([1, 2, 3]), [2, 4, 6]);
  });
  it('passes context to functions', function() {
    function x(val) {
      return this.x * val;
    }
    function y(val) {
      return this.y * val;
    }
    function z(val) {
      return this.z * val;
    }
    var context = {
      a: R.pipe(x, y, z),
      x: 4,
      y: 2,
      z: 1
    };
    eq(context.a(5), 40);
  });
  it('can be applied to one argument', function() {
    var f = function(a, b, c) { return [a, b, c]; };
    var g = R.pipe(f);
    eq(g.length, 3);
    eq(g(1, 2, 3), [1, 2, 3]);
  });
});

piped

piped<T>(input: any, ...fnList: Func<any>[]): T

It is basically R.pipe, but instead of passing input argument as R.pipe(...)(input), you pass it as the first argument.

const result = piped(
  [1, 2, 3],
  R.filter(x => x > 1),
  R.map(x => x*10),
)
// => [20, 30]

Try the above R.piped example in Rambda REPL

All Typescript definitions

piped<T>(input: any, ...fnList: Func<any>[]): T;

R.piped source

import { pipe } from './pipe'

export function piped(...inputs){
  const [ input, ...fnList ] = inputs

  return pipe(...fnList)(input)
}

Tests

import { add } from './add'
import { filter } from './filter'
import { map } from './map'
import { piped } from './piped'

test('happy', () => {
  const result = piped(
    [ 1, 2, 3 ],
    filter(x => x > 1),
    map(x => x * 10),
    map(add(1))
  )
  const expectedResult = [ 21, 31 ]

  expect(result).toEqual(expectedResult)
})

pipedAsync

pipedAsync<T>(
  input: any,
  ...fns: (Func<any> | Async<any>)[]
): Promise<T>

All Typescript definitions

pipedAsync<T>(
  input: any,
  ...fns: (Func<any> | Async<any>)[]
): Promise<T>;

pluck

pluck<T>(property: number, list: ReadonlyArray<T>): T

It returns list of the values of property taken from the all objects inside list.

const list = [{a: 1}, {a: 2}, {b: 3}]
const property = 'a'

R.pluck(list, property) 
// => [1, 2]

Try the above R.pluck example in Rambda REPL

All Typescript definitions

pluck<T>(property: number, list: ReadonlyArray<T>): T;
pluck<K extends keyof T, T>(property: K, list: ReadonlyArray<T>): T[K][];
pluck(property: number): <T>(list: ReadonlyArray<T>) => T;
pluck<P extends string>(property: P): <T>(list: ReadonlyArray<Record<P, T>>) => T[];

R.pluck source

import { map } from './map'

export function pluck(property, list){
  if (arguments.length === 1) return _list => pluck(property, _list)

  const willReturn = []

  map(x => {
    if (x[ property ] !== undefined){
      willReturn.push(x[ property ])
    }
  }, list)

  return willReturn
}

Tests

import { pluck } from './pluck'

test('happy', () => {
  expect(pluck('a')([ { a : 1 }, { a : 2 }, { b : 1 } ])).toEqual([ 1, 2 ])
})

test('with number', () => {
  const input = [
    [ 1, 2 ],
    [ 3, 4 ],
  ]

  expect(pluck(0, input)).toEqual([ 1, 3 ])
})

Typescript test

import {pluck} from 'rambda'

describe('pluck', () => {
  it('with object', () => {
    interface ListMember {
      a: number,
      b: string,
    }
    const input: ListMember[] = [
      {a: 1, b: 'foo'},
      {a: 2, b: 'bar'},
    ]
    const resultA = pluck('a', input)
    const resultB = pluck('b')(input)
    resultA // $ExpectType number[]
    resultB // $ExpectType string[]
  })

  it('with array', () => {
    const input = [
      [1, 2],
      [3, 4],
      [5, 6],
    ]
    const result = pluck(0, input)
    const resultCurry = pluck(0)(input)
    result // $ExpectType number[]
    resultCurry // $ExpectType number[]
  })
})

1 failed Ramda.pluck specs

💥 Reason for the failure: ramda method behaves as a transducer

var R = require('../../../../dist/rambda.js');
var eq = require('./shared/eq');

describe('pluck', function() {
  var people = [
    {name: 'Fred', age: 23},
    {name: 'Wilma', age: 21},
    {name: 'Pebbles', age: 2}
  ];
  it('behaves as a transducer when given a transducer in list position', function() {
    var numbers = [{a: 1}, {a: 2}, {a: 3}, {a: 4}];
    var transducer = R.compose(R.pluck('a'), R.map(R.add(1)), R.take(2));
    eq(R.transduce(transducer, R.flip(R.append), [], numbers), [2, 3]);
  });
});

prepend

prepend<T>(x: T, listOrString: ReadonlyArray<T>): T[]

It adds element x at the beginning of listOrString.

const x = 'foo'

const result = [
  R.prepend(x, '_cherry'),
  R.prepend(x, ['bar', 'baz'])
]
// => ['foo_cherry', ['foo', 'bar', 'baz']]

Try the above R.prepend example in Rambda REPL

All Typescript definitions

prepend<T>(x: T, listOrString: ReadonlyArray<T>): T[];
prepend<T>(x: T): (listOrString: ReadonlyArray<T>) => T[];

R.prepend source

export function prepend(x, listOrString){
  if (arguments.length === 1)
    return _listOrString => prepend(x, _listOrString)

  if (typeof listOrString === 'string') return `${ x }${ listOrString }`

  return [ x ].concat(listOrString)
}

Tests

import { prepend } from './prepend'

test('happy', () => {
  expect(prepend('f', 'oo')).toEqual('foo')
})

test('prepend', () => {
  expect(prepend('yes', [ 'foo', 'bar', 'baz' ])).toEqual([
    'yes',
    'foo',
    'bar',
    'baz',
  ])

  expect(prepend('foo')([])).toEqual([ 'foo' ])
})

prevIndex

prevIndex(index: number, list: any[]): number

It returns the next index of the list when the order is descending.

If we have reached the beginning of the list, then it will return the last index of the list.

const list = [1, 2, 3]

const result = [
  R.prevIndex(0, list),
  R.prevIndex(1, list),
  R.prevIndex(2, list),
]
// => [2, 0, 1]

Try the above R.prevIndex example in Rambda REPL

All Typescript definitions

prevIndex(index: number, list: any[]): number;

R.prevIndex source

export function prevIndex(index, list){
  return index === 0 ? list.length - 1 : index - 1
}

Tests

import { prevIndex } from './prevIndex'

const list = [ 1, 2, 3, 4 ]

test('happy path 1', () => {
  expect(prevIndex(2, list)).toEqual(1)
})

test('happy path 2', () => {
  expect(prevIndex(0, list)).toEqual(3)
})

produce

produce<T>(
  rules: any,
  input: any
): T

It returns an object created by applying each value of rules to input argument

rules input is an object with synchronous or asynchronous functions as values.

If there is at least one member of rules that is asynchronous, then the return value is a promise.

const rules = {
  foo: x =>  > 10,
  bar: x => ({baz: x})
}
const input = 7
const result = R.produce(rules, input)

const expected = {
  foo: false,
  bar: {baz: 7}
}
// => `result` is equal to `expected`

Try the above R.produce example in Rambda REPL

All Typescript definitions

produce<T>(
  rules: any,
  input: any
): T;
produce<T>(
  rules: any,
): (input: any) => T;

R.produce source

import { map } from './map'
import { type } from './type'

function helper({ condition, inputArgument, prop }){
  return new Promise((resolve, reject) => {
    if (type(condition) !== 'Async'){
      return resolve({
        type    : prop,
        payload : condition(inputArgument),
      })
    }

    condition(inputArgument)
      .then(result => {
        resolve({
          type    : prop,
          payload : result,
        })
      })
      .catch(err => reject(err))
  })
}

export function produce(conditions, inputArgument){
  if (arguments.length === 1){
    return inputArgumentHolder => produce(conditions, inputArgumentHolder)
  }
  let asyncConditionsFlag = false
  for (const prop in conditions){
    if (
      asyncConditionsFlag === false &&
      type(conditions[ prop ]) === 'Async'
    ){
      asyncConditionsFlag = true
    }
  }

  if (asyncConditionsFlag === false){
    const willReturn = {}
    for (const prop in conditions){
      willReturn[ prop ] = conditions[ prop ](inputArgument)
    }

    return willReturn
  }

  const promised = []
  for (const prop in conditions){
    const condition = conditions[ prop ]
    promised.push(helper({
      inputArgument,
      condition,
      prop,
    }))
  }

  return new Promise((resolve, reject) => {
    Promise.all(promised)
      .then(results => {
        const willReturn = {}

        map(result => willReturn[ result.type ] = result.payload, results)

        resolve(willReturn)
      })
      .catch(err => reject(err))
  })
}

Tests

import { delay } from './delay'
import { produce } from './produce'

test('async', async () => {
  const fn = produce({
    foo : async x => {
      await delay(100)

      return `${ x }_ZEPPELIN`
    },
    bar : inputArgument => inputArgument === 5,
  })
  const expected = {
    foo : 'LED_ZEPPELIN',
    bar : false,
  }

  const result = await fn('LED')
  expect(result).toEqual(expected)
})

test('async with error', async () => {
  const fn = produce({
    foo : async x => {
      await delay(100)
      throw new Error(`${ x }_ZEPPELIN`)
    },
    bar : inputArgument => inputArgument === 5,
  })

  try {
    await fn('LED')
    expect(1).toBe(2)
  } catch (e){
    expect(e.message).toBe('LED_ZEPPELIN')
  }
})

test('sync', () => {
  const fn = produce({
    foo : x => x + 1,
    bar : inputArgument => inputArgument === 5,
  })
  const expected = {
    foo : 6,
    bar : true,
  }

  const result = fn(5)
  expect(result).toEqual(expected)
})

product

product(list: ReadonlyArray<number>): number

R.product([ 2, 3, 4 ])
// => 24)

Try the above R.product example in Rambda REPL

All Typescript definitions

product(list: ReadonlyArray<number>): number;

R.product source

import { multiply } from './multiply'
import { reduce } from './reduce'

export const product = reduce(multiply, 1)

Tests

import { product } from './product'

test('happy', () => {
  expect(product([ 2, 3, 4 ])).toEqual(24)
})

test('bad input', () => {
  expect(product([ null ])).toEqual(0)
  expect(product([])).toEqual(1)
})

promiseAllObject

promiseAllObject<T>(
  input: ObjectWithPromises
): Promise<T>

Promise.all version, which accept object of asynchronous functions as input.

const fn = ms => new Promise(resolve => {
  setTimeout(() => {
    resolve(ms + 10)
  }, ms)
})
const promises = {
  a : fn(1),
  b : fn(2),
}

const result = R.promiseAllObject(promises)
const expected = { a:11, b:12 }
// `result` resolves to `expected`

Try the above R.promiseAllObject example in Rambda REPL

All Typescript definitions

promiseAllObject<T>(
  input: ObjectWithPromises
): Promise<T>;

R.promiseAllObject source

export function promiseAllObject(promises){
  return new Promise((res, rej) => {
    let counter = 0
    const props = {}
    const promisedArr = []

    for (const prop in promises){
      props[ counter ] = prop
      promisedArr.push(promises[ prop ])
      counter++
    }

    Promise.all(promisedArr)
      .then(result => {
        const willReturn = {}
        result.map((val, key) => {
          const prop = props[ key ]
          willReturn[ prop ] = val
        })

        res(willReturn)
      })
      .catch(rej)
  })
}

Tests

import { promiseAllObject } from './promiseAllObject'

test('happy', async () => {
  const delay = ms =>
    new Promise(res => {
      setTimeout(() => {
        res(ms)
      }, ms)
    })
  const promises = {
    a : delay(1),
    b : delay(2),
    c : delay(3),
  }
  const result = await promiseAllObject(promises)

  expect(result).toEqual({
    a : 1,
    b : 2,
    c : 3,
  })
})

prop

prop<P extends keyof T, T>(propToFind: P, obj: T): T[P]

It returns the value of property propToFind in obj.

If there is no such property, it returns undefined.

const result = [
  R.prop('x', {x: 100}), 
  R.prop('x', {a: 1}) 
]
// => [100, undefined]

Try the above R.prop example in Rambda REPL

All Typescript definitions

prop<P extends keyof T, T>(propToFind: P, obj: T): T[P];
prop<P extends string>(p: P): <T>(propToFind: Record<P, T>) => T;
prop<P extends string, T>(p: P): (propToFind: Record<P, T>) => T;

R.prop source

export function prop(propToFind, obj){
  if (arguments.length === 1) return _obj => prop(propToFind, _obj)

  if (!obj) return undefined

  return obj[ propToFind ]
}

Tests

import { prop } from './prop'

test('prop', () => {
  expect(prop('foo')({ foo : 'baz' })).toEqual('baz')

  expect(prop('bar')({ foo : 'baz' })).toEqual(undefined)

  expect(prop('bar')(null)).toEqual(undefined)
})

propEq

propEq<T, K extends keyof T>(propToFind: K, valueToMatch: T[K], obj: T): boolean

It returns true if obj has property propToFind and its value is equal to valueToMatch.

const obj = { foo: 'bar' }
const secondObj = { foo: 1 }

const propToFind = 'foo'
const valueToMatch = 'bar'

const result = [
  R.propEq(propToFind, valueToMatch, obj),
  R.propEq(propToFind, valueToMatch, secondObj)
]
// => [true, false]

Try the above R.propEq example in Rambda REPL

All Typescript definitions

propEq<T, K extends keyof T>(propToFind: K, valueToMatch: T[K], obj: T): boolean;
propEq<T, K extends keyof T>(propToFind: K, valueToMatch: T[K]): (obj: T) => boolean;
propEq<T, K extends keyof T>(propToFind: K): {
   (valueToMatch: T[K], obj: T): boolean;
   (valueToMatch: T[K]): (obj: T) => boolean;
};

R.propEq source

import { curry } from './curry'

function propEqFn(
  propToFind, valueToMatch, obj
){
  if (!obj) return false

  return obj[ propToFind ] === valueToMatch
}

export const propEq = curry(propEqFn)

Tests

import { propEq } from './propEq'

test('happy', () => {
  expect(propEq('foo', 'bar')({ foo : 'bar' })).toBeTrue()
  expect(propEq('foo', 'bar')({ foo : 'baz' })).toBeFalse()
  expect(propEq('foo')('bar')({ foo : 'baz' })).toBeFalse()
  expect(propEq(
    'foo', 'bar', null
  )).toBeFalse()
})

Typescript test

import {propEq} from 'rambda'

const property = 'foo'
const numberProperty = 1
const value = 'bar'
const obj = {[property]: value}
const objWithNumberIndex = {[numberProperty]: value}

describe('propEq', () => {
  it('happy', () => {
    const result = propEq(property, value, obj)
    result // $ExpectType boolean
  })
  it('number is property', () => {
    const result = propEq(1, value, objWithNumberIndex)
    result // $ExpectType boolean
  })
  it('with optional property', () => {
    interface MyType {
      optional?: string | number,
    }

    const myObject: MyType = {}
    const valueToFind = '1111'
    const optionalValueToFind: string | number | undefined = '1111'
    const result = propEq('optional', valueToFind, myObject)
    const result2 = propEq('optional', optionalValueToFind, myObject)
    result // $ExpectType boolean
    result2 // $ExpectType boolean
  })
})

1 failed Ramda.propEq specs

💥 Reason for the failure: ramda method pass to equals method if available

var R = require('../../../../dist/rambda.js');
var eq = require('./shared/eq');

describe('propEq', function() {
  var obj1 = {name: 'Abby', age: 7, hair: 'blond'};
  var obj2 = {name: 'Fred', age: 12, hair: 'brown'};
  it('handles number as property', function() {
    var deities = ['Cthulhu', 'Dagon', 'Yog-Sothoth'];
    eq(R.propEq(0, 'Cthulhu', deities), true);
    eq(R.propEq(1, 'Dagon', deities), true);
    eq(R.propEq(2, 'Yog-Sothoth', deities), true);
    eq(R.propEq(-1, 'Yog-Sothoth', deities), true);
    eq(R.propEq(3, undefined, deities), true);
  });
  it('has R.equals semantics', function() {
    function Just(x) { this.value = x; }
    Just.prototype.equals = function(x) {
      return x instanceof Just && R.equals(x.value, this.value);
    };
    eq(R.propEq('value', 0, {value: -0}), false);
    eq(R.propEq('value', -0, {value: 0}), false);
    eq(R.propEq('value', NaN, {value: NaN}), true);
    eq(R.propEq('value', new Just([42]), {value: new Just([42])}), true);
  });
});

propIs

propIs(type: any, name: string, obj: any): boolean

It returns true if property of obj is from target type.

const obj = {a:1, b: 'foo'}
const property = 'foo'

const result = [
  R.propIs(String, property, obj),
  R.propIs(Number, property, obj)
]
// => [true, false]

Try the above R.propIs example in Rambda REPL

All Typescript definitions

propIs(type: any, name: string, obj: any): boolean;
propIs(type: any, name: string): (obj: any) => boolean;
propIs(type: any): {
    (name: string, obj: any): boolean;
    (name: string): (obj: any) => boolean;
};

R.propIs source

import { curry } from './curry'
import { is } from './is'

function propIsFn(
  targetPrototype, property, obj
){
  return is(targetPrototype, obj[ property ])
}

export const propIs = curry(propIsFn)

Tests

import { propIs } from './propIs'

const obj = { value : 1 }
const property = 'value'

test('when true', () => {
  expect(propIs(
    Number, property, obj
  )).toBeTrue()
})

test('when false', () => {
  expect(propIs(
    String, property, obj
  )).toBeFalse()
  expect(propIs(
    String, property, {}
  )).toBeFalse()
})

Typescript test

import {propIs} from 'rambda'

const property = 'a'
const obj = {a: 1}

describe('propIs', () => {
  it('happy', () => {
    const result = propIs(Number, property, obj)
    result // $ExpectType boolean
  })

  it('curried', () => {
    const result = propIs(Number, property)(obj)
    result // $ExpectType boolean
  })
})

propOr

propOr<T, U, V>(defaultValue: T, property: string, obj: U): V

It returns either defaultValue or the value of property in obj.

const obj = {a: 1}
const defaultValue = 'DEFAULT_VALUE'
const property = 'a'

const result = [
  R.propOr(defaultValue, property, obj),
  R.propOr(defaultValue, 'foo', obj)
]
// => [1, 'DEFAULT_VALUE']

Try the above R.propOr example in Rambda REPL

All Typescript definitions

propOr<T, U, V>(defaultValue: T, property: string, obj: U): V;
propOr<T>(defaultValue: T, property: string): <U, V>(obj: U) => V;
propOr<T>(defaultValue: T): <U, V>(property: string, obj: U) => V;

R.propOr source

import { curry } from './curry'
import { defaultTo } from './defaultTo'

function propOrFn(
  defaultValue, property, obj
){
  if (!obj) return defaultValue

  return defaultTo(defaultValue, obj[ property ])
}

export const propOr = curry(propOrFn)

Tests

import { propOr } from './propOr'

test('propOr (result)', () => {
  const obj = { a : 1 }
  expect(propOr(
    'default', 'a', obj
  )).toEqual(1)
  expect(propOr(
    'default', 'notExist', obj
  )).toEqual('default')
  expect(propOr(
    'default', 'notExist', null
  )).toEqual('default')
})

test('propOr (currying)', () => {
  const obj = { a : 1 }
  expect(propOr('default')('a', obj)).toEqual(1)
  expect(propOr('default', 'a')(obj)).toEqual(1)
  expect(propOr('default')('notExist', obj)).toEqual('default')
  expect(propOr('default', 'notExist')(obj)).toEqual('default')
})

random

random(minInclusive: number, maxInclusive: number): number

It returns a random number between min inclusive and max inclusive.

All Typescript definitions

random(minInclusive: number, maxInclusive: number): number;

R.random source

export function random(min, max){
  return Math.floor(Math.random() * (max - min + 1)) + min
}

Tests

import {random} from './random'
import {range} from './range'

test('when returns true', () => {
  range(0, 100).map(() => {
    const randomResult = random(1, 10)
    expect(randomResult).toBeLessThanOrEqual(10)
    expect(randomResult).toBeGreaterThanOrEqual(1)
  })
})

randomString

randomString(length?: number, alphabetOnlyFlag?: boolean): string

All Typescript definitions

randomString(length?: number, alphabetOnlyFlag?: boolean): string;

R.randomString source

import { head } from './head'
import { range } from './range'
import { shuffle } from './shuffle'

const charCodesString = [ ...range(65, 90), ...range(97, 122) ]
const charCodes = [ ...charCodesString, ...range(49, 57) ]

export function randomString(length = 8, stringTag = false){
  const loops = range(0, length)
  const charSet = stringTag ? charCodesString : charCodes

  return loops.map(x => String.fromCharCode(head(shuffle(charSet)))).join('')
}

Tests

import { randomString } from './randomString'

test('happy', () => {
  expect(randomString().length).toBe(8)
})

test('with length', () => {
  expect(randomString(3).length).toBe(3)
})

test('only string randomString', () => {
  expect(randomString(3, true).length).toBe(3)
})

range

range(start: number, end: number): number[]

It returns list of numbers between start(inclusive) to end(exclusive) numbers.

R.range(0, 5)
// => [0, 1, 2, 3, 4]

Try the above R.range example in Rambda REPL

All Typescript definitions

range(start: number, end: number): number[];
range(start: number): (end: number) => number[];

R.range source

export function range(start, end){
  if (arguments.length === 1) return _end => range(start, _end)

  if (Number.isNaN(Number(start)) || Number.isNaN(Number(end))){
    throw new TypeError('Both arguments to range must be numbers')
  }

  if (end < start) return []

  const len = end - start
  const willReturn = Array(len)

  for (let i = 0; i < len; i++){
    willReturn[ i ] = start + i
  }

  return willReturn
}

Tests

import { range } from './range'

test('happy', () => {
  expect(range(0, 10)).toEqual([ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 ])
})

test('end range is bigger than start range', () => {
  expect(range(7, 3)).toEqual([])
  expect(range(5, 5)).toEqual([])
})

test('with bad input', () => {
  const throwMessage = 'Both arguments to range must be numbers'
  expect(() => range('a', 6)).toThrow(throwMessage)
  expect(() => range(6, 'z')).toThrow(throwMessage)
})

test('curry', () => {
  expect(range(0)(10)).toEqual([ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 ])
})

reduce

reduce<T, TResult>(reducer: (prev: TResult, current: T, i: number) => TResult, initialValue: TResult, list: ReadonlyArray<T>): TResult

const list = [1, 2, 3]
const initialValue = 10
const reducer = (prev, current) => prev * current

const result = R.reduce(reducer, initialValue, list)
// => 60

Try the above R.reduce example in Rambda REPL

All Typescript definitions

reduce<T, TResult>(reducer: (prev: TResult, current: T, i: number) => TResult, initialValue: TResult, list: ReadonlyArray<T>): TResult;
reduce<T, TResult>(reducer: (prev: TResult, current: T) => TResult, initialValue: TResult, list: ReadonlyArray<T>): TResult;
reduce<T, TResult>(reducer: (prev: TResult, current: T, i?: number) => TResult): (initialValue: TResult, list: ReadonlyArray<T>) => TResult;
reduce<T, TResult>(reducer: (prev: TResult, current: T, i?: number) => TResult, initialValue: TResult): (list: ReadonlyArray<T>) => TResult;

R.reduce source

import { curry } from './curry'
import { _isArray } from './_internals/_isArray'
import { _keys } from './_internals/_keys'

function reduceFn(
  reducer, acc, list
){
  if (list === undefined){
    return acc
  }

  if (_isArray(list)){
    let index = 0
    const len = list.length

    while (index < len){
      acc = reducer(acc, list[ index ], index, list)
      index++
    }
  } else {
    let index = 0
    const keys = _keys(list)
    const len = keys.length

    while (index < len){
      const key = keys[ index ]
      acc = reducer(acc, key, list[ key ], list)
      index++
    }
  }

  return acc
}

export const reduce = curry(reduceFn)

Tests

import { reduce } from './reduce'

test('happy', () => {
  const reducer = (
    prev, current, i
  ) => {
    expect(i).toBeNumber()

    return prev + current
  }
  const initialValue = 1
  const list = [ 1, 2, 3 ]

  expect(reduce(
    reducer, initialValue, list
  )).toEqual(7)
})

Typescript test

import {reduce} from 'rambda'

describe('reduce', () => {
  it('happy', () => {
    const result = reduce<number, number>(
      (acc, elem) => {
        acc // $ExpectType number
        elem // $ExpectType number
        return acc + elem
      },
      1,
      [1, 2, 3]
    )

    result // $ExpectType number
  })

  it('with two types', () => {
    const result = reduce<number, string>(
      (acc, elem) => {
        acc // $ExpectType string
        elem // $ExpectType number

        return `${acc}${elem}`
      },
      'foo',
      [1, 2, 3]
    )

    result // $ExpectType string
  })

  it('with index', () => {
    const result = reduce<number, number>(
      (acc, elem, i) => {
        acc // $ExpectType number
        elem // $ExpectType number
        i // $ExpectType number
        return acc + elem
      },
      1,
      [1, 2, 3]
    )

    result // $ExpectType number
  })

  it('fallback', () => {
    const result = reduce(
      (acc, val) => {
        acc // $ExpectType number
        return acc + val
      },
      1,
      [1, 2, 3]
    )

    result // $ExpectType number
  })

  it('fallback with index', () => {
    const result = reduce(
      (acc, val, i) => {
        acc // $ExpectType number
        i // $ExpectType number
        return acc + val
      },
      1,
      [1, 2, 3]
    )

    result // $ExpectType number
  })

  it('fallback with two types', () => {
    const result = reduce(
      (acc, val) => {
        acc // $ExpectType string
        return acc + val
      },
      'foo',
      [1, 2, 3]
    )

    result // $ExpectType string
  })
})

2 failed Ramda.reduce specs

💥 Reason for the failure: rambda doesn't have R.reduced method | ramda method pass to reduce method

var R = require('../../../../dist/rambda.js');
var eq = require('./shared/eq');

describe('reduce', function() {
  var add = function(a, b) {return a + b;};
  var mult = function(a, b) {return a * b;};
  it('Prefers the use of the iterator of an object over reduce (and handles short-circuits)', function() {
    var symIterator = (typeof Symbol !== 'undefined') ? Symbol.iterator : '@@iterator';
    function Reducible(arr) {
      this.arr = arr;
    }
    Reducible.prototype.reduce = function(f, init) {
      var acc = init;
      for (var i = 0; i < this.arr.length; i += 1) {
        acc = f(acc, this.arr[i]);
      }
      return acc;
    };
    Reducible.prototype[symIterator] = function() {
      var a = this.arr;
      return {
        _pos: 0,
        next: function() {
          if (this._pos < a.length) {
            var v = a[this._pos];
            this._pos += 1;
            return {
              value: v,
              done: false
            };
          } else {
            return {
              done: true
            };
          }
        }
      };
    };
    var xf = R.take(2);
    var apendingT = { };
    apendingT['@@transducer/result'] = R.identity;
    apendingT['@@transducer/step'] = R.flip(R.append);
    var rfn = xf(apendingT);
    var list = new Reducible([1, 2, 3, 4, 5, 6]);
    eq(R.reduce(rfn, [], list), [1, 2]);
  });
  it('short circuits with reduced', function() {
    var addWithMaxOf10 = function(acc, val) {return acc + val > 10 ? R.reduced(acc) : acc + val;};
    eq(R.reduce(addWithMaxOf10, 0, [1, 2, 3, 4]), 10);
    eq(R.reduce(addWithMaxOf10, 0, [2, 4, 6, 8]), 6);
  });
});

reject

reject<T>(predicate: FilterFunctionArray<T>): (x: T[]) => T[]

It has the opposite effect of R.filter.

It will return those members of list that return false when applied to predicate function.

const list = [1, 2, 3, 4]
const predicate = x => x > 2

const result = [
  R.reject(predicate, list)
]
// => [1, 2]

Try the above R.reject example in Rambda REPL

All Typescript definitions

reject<T>(predicate: FilterFunctionArray<T>): (x: T[]) => T[];
reject<T>(predicate: FilterFunctionArray<T>, x: T[]): T[];
reject<T, U>(predicate: FilterFunctionObject<T>): (x: Dictionary<T>) => Dictionary<T>;
reject<T>(predicate: FilterFunctionObject<T>, x: Dictionary<T>): Dictionary<T>;

R.reject source

import { filter } from './filter'

export function reject(predicate, list){
  if (arguments.length === 1) return _list => reject(predicate, _list)

  return filter((x, i) => !predicate(x, i), list)
}

Tests

import { reject } from './reject'

const isOdd = n => n % 2 === 1

test('with array', () => {
  expect(reject(isOdd, [ 1, 2, 3, 4 ])).toEqual([ 2, 4 ])
})

test('with object', () => {
  expect(reject(isOdd, {
    a : 1,
    b : 2,
    c : 3,
    d : 4,
  })).toEqual({
    b : 2,
    d : 4,
  })
})

test('pass index as second argument', () => {
  reject((x, i) => {
    expect(typeof x).toBe('number')
    expect(typeof i).toBe('number')
  },
  [ 10, 12, 15 ])
})

Typescript test

import {reject} from 'rambda'

describe('reject with array', () => {
  it('1 curry', () => {
    const x = reject<number>(a => {
      a // $ExpectType number
      return a > 1
    })([1, 2, 3])
    x // $ExpectType number[]
  })
  it('1', () => {
    const x = reject<number>(
      a => {
        a // $ExpectType number
        return a > 1
      },
      [1, 2, 3]
    )
    x // $ExpectType number[]
  })
  it('2', () => {
    const x = reject<number>(
      (a, b) => {
        a // $ExpectType number
        return a > 1
      },
      [1, 2, 3]
    )
    x // $ExpectType number[]
  })
})

describe('reject with objects', () => {
  it('curry', () => {
    const x = reject<number, number>((a, b, c) => {
      b // $ExpectType string
      c // $ExpectType Dictionary<number>

      return a > 1
    })({a: 1, b: 2})
    x // $ExpectType Dictionary<number>
  })

  it('object with three arguments predicate', () => {
    const x = reject<number>(
      (a, b, c) => {
        b // $ExpectType string
        c // $ExpectType Dictionary<number>

        return a > 1
      },
      {a: 1, b: 2}
    )
    x // $ExpectType Dictionary<number>
  })

  it('object with two arguments predicate', () => {
    const x = reject<number>(
      (a, b) => {
        b // $ExpectType string
        return a > 1
      },
      {a: 1, b: 2}
    )
    x // $ExpectType Dictionary<number>
  })
  it('object with one argument predicate', () => {
    const x = reject<number>(
      a => {
        a // $ExpectType number
        return a > 1
      },
      {a: 1, b: 2}
    )
    x // $ExpectType Dictionary<number>
  })
})

1 failed Ramda.reject specs

💥 Reason for the failure: ramda method dispatches to filter method

var R = require('../../../../dist/rambda.js');
var eq = require('./shared/eq');

describe('reject', function() {
  var even = function(x) {return x % 2 === 0;};
  it('dispatches to `filter` method', function() {
    function Nothing() {}
    Nothing.value = new Nothing();
    Nothing.prototype.filter = function() {
      return this;
    };
    function Just(x) { this.value = x; }
    Just.prototype.filter = function(pred) {
      return pred(this.value) ? this : Nothing.value;
    };
    var m = new Just(42);
    eq(R.filter(R.T, m), m);
    eq(R.filter(R.F, m), Nothing.value);
    eq(R.reject(R.T, m), Nothing.value);
    eq(R.reject(R.F, m), m);
  });
});

remove

remove(
  toRemove: string | RegExp | (string | RegExp)[],
  text: string
): string

It will remove all toRemove entries from text sequentially.

toRemove argument can be either a list of strings/regular expressions or a single string/regular expression.

const result = remove(
  ['foo','bar'],
  'foo bar baz foo'
)
// => 'baz foo'

Try the above R.remove example in Rambda REPL

All Typescript definitions

remove(
  toRemove: string | RegExp | (string | RegExp)[],
  text: string
): string;
remove(
  toRemove: string | RegExp | (string | RegExp)[]
): (text: string) => string;

R.remove source

import { replace } from './replace'
import { type } from './type'

export function remove(inputs, text){
  if (arguments.length === 1){
    return textHolder => remove(inputs, textHolder)
  }

  if (type(text) !== 'String'){
    throw new Error(`R.remove requires string not ${ type(text) }`)
  }

  if (type(inputs) !== 'Array'){
    return replace(
      inputs, '', text
    ).trim()
  }

  let textCopy = text

  inputs.forEach(singleInput => {
    textCopy = replace(
      singleInput, '', textCopy
    ).trim()
  })

  return textCopy
}

Tests

import { remove } from './remove'

test('happy', () => {
  const inputs = [ /foo/, /not\shere/, /also/, 'bar' ]
  const text = 'foo bar baz foo'

  const result = remove(inputs)(text)
  const expectedResult = 'baz foo'

  expect(result).toEqual(expectedResult)
})

test('with strings + curry', () => {
  const inputs = [ 'foo', 'bar' ]
  const text = 'foo bar baz foo'

  const result = remove(inputs)(text)
  const expectedResult = 'baz foo'

  expect(result).toEqual(expectedResult)
})

test('with strings and regex', () => {
  const inputs = [ /foo/g, 'bar' ]
  const text = 'foo bar baz foo'

  const result = remove(inputs, text)
  const expectedResult = 'baz'

  expect(result).toEqual(expectedResult)
})

test('text is not string', () => {
  const inputs = [ /foo/g, 'bar' ]
  const text = null

  expect(() => remove(inputs, text)).toThrow()
})

test('with regexes', () => {
  const inputs = [ /foo/g, /bar/ ]
  const text = 'foo bar baz foo'

  const result = remove(inputs, text)
  const expectedResult = 'baz'

  expect(result).toEqual(expectedResult)
})

test('with single rule', () => {
  const inputs = /foo/g
  const text = 'foo bar baz foo'

  const result = remove(inputs, text)
  const expectedResult = 'bar baz'

  expect(result).toEqual(expectedResult)
})

renameProps

renameProps(rules: object, input: object): object

If property prop of rules is also a property in input, then rename input property to rules[prop].

All Typescript definitions

renameProps(rules: object, input: object): object;
renameProps(rules: object): (input: object) => object;

R.renameProps source

import { merge } from './merge'
import { omit } from './omit'

export function renameProps(conditions, inputObject){
  if (inputObject === undefined){
    return inputObjectHolder => renameProps(conditions, inputObjectHolder)
  }
  const renamed = {}
  Object.keys(conditions).forEach(renameConditionProp => {
    if (Object.keys(inputObject).includes(renameConditionProp)){
      renamed[ conditions[ renameConditionProp ] ] =
        inputObject[ renameConditionProp ]
    }
  })

  return merge(renamed, omit(Object.keys(conditions), inputObject))
}

Tests

import { renameProps } from './renameProps'

test('renameProps', () => {
  const rules = {
    f : 'foo',
    b : 'bar',
  }
  const input = {
    f : 1,
    b : 2,
  }
  const result = renameProps(rules, input)
  const expectedResult = {
    foo : 1,
    bar : 2,
  }
  expect(result).toEqual(expectedResult)
})

test('curry', () => {
  const rules = {
    f : 'foo',
    b : 'bar',
  }
  const input = {
    f : 1,
    b : 2,
  }
  const result = renameProps(rules)(input)
  const expectedResult = {
    foo : 1,
    bar : 2,
  }
  expect(result).toEqual(expectedResult)
})

repeat

repeat<T>(x: T, timesToRepeat: number): T[]

It returns a list of x input repeated timesToRepeat input.

R.repeat('foo', 3)
// => ['foo', 'foo', 'foo']

Try the above R.repeat example in Rambda REPL

All Typescript definitions

repeat<T>(x: T, timesToRepeat: number): T[];
repeat<T>(x: T): (timesToRepeat: number) => T[];

R.repeat source

export function repeat(x, timesToRepeat){
  if (arguments.length === 1){
    return _timesToRepeat => repeat(x, _timesToRepeat)
  }

  return Array(timesToRepeat).fill(x)
}

Tests

import { repeat } from './repeat'

test('repeat', () => {
  expect(repeat('')(3)).toEqual([ '', '', '' ])
  expect(repeat('foo', 3)).toEqual([ 'foo', 'foo', 'foo' ])

  const obj = {}
  const arr = repeat(obj, 3)

  expect(arr).toEqual([ {}, {}, {} ])

  expect(arr[ 0 ] === arr[ 1 ]).toBeTrue()
})

replace

replace(strOrRegex: RegExp | string, replacer: string, str: string): string

It replaces strOrRegex found in str with replacer.

const strOrRegex = /o/g

const result = R.replace(strOrRegex, '|0|', 'foo')
// => 'f|0||0|'

Try the above R.replace example in Rambda REPL

All Typescript definitions

replace(strOrRegex: RegExp | string, replacer: string, str: string): string;
replace(strOrRegex: RegExp | string, replacer: string): (str: string) => string;
replace(strOrRegex: RegExp | string): (replacer: string) => (str: string) => string;

R.replace source

export function replace(
  pattern, replacer, str
){
  if (replacer === undefined){
    return (_replacer, _str) => replace(
      pattern, _replacer, _str
    )
  } else if (str === undefined){
    return _str => replace(
      pattern, replacer, _str
    )
  }

  return str.replace(pattern, replacer)
}

Tests

import { replace } from './replace'

test('happy', () => {
  expect(replace(
    'foo', 'yes', 'foo bar baz'
  )).toEqual('yes bar baz')
})

test('1', () => {
  expect(replace(/\s/g)('|')('foo bar baz')).toEqual('foo|bar|baz')
})

test('2', () => {
  expect(replace(/\s/g)('|', 'foo bar baz')).toEqual('foo|bar|baz')
})

test('3', () => {
  expect(replace(/\s/g, '|')('foo bar baz')).toEqual('foo|bar|baz')
})

reset

reset(): void

All Typescript definitions

reset(): void;

reverse

reverse<T>(listOrString: ReadonlyArray<T>): T[]

It returns a reversed copy of listOrString input.

const result = [
  R.reverse('foo'),
  R.reverse([1, 2, 3])
]
// => ['oof', [3, 2, 1]

Try the above R.reverse example in Rambda REPL

All Typescript definitions

reverse<T>(listOrString: ReadonlyArray<T>): T[];
reverse(listOrString: string): string;

R.reverse source

export function reverse(listOrString){
  if (typeof listOrString === 'string'){
    return listOrString.split('').reverse()
      .join('')
  }

  const clone = listOrString.slice()

  return clone.reverse()
}

Tests

import { reverse } from './reverse'

test('happy', () => {
  expect(reverse([ 1, 2, 3 ])).toEqual([ 3, 2, 1 ])
})

test('with string', () => {
  expect(reverse('baz')).toEqual('zab')
})

test('it doesn\'t mutate', () => {
  const arr = [ 1, 2, 3 ]

  expect(reverse(arr)).toEqual([ 3, 2, 1 ])

  expect(arr).toEqual([ 1, 2, 3 ])
})

set

set<T, U>(lens: Lens, replacer: U, obj: T): T

It returns a copied Object or Array with modified lens focus set to replacer value.

const input = {x: 1, y: 2}
const xLens = R.lensProp('x')

R.set(xLens, 4, input) //=> {x: 4, y: 2}
R.set(xLens, 8, input) //=> {x: 8, y: 2}

Try the above R.set example in Rambda REPL

All Typescript definitions

set<T, U>(lens: Lens, replacer: U, obj: T): T;
set<U>(lens: Lens, replacer: U): <T>(obj: T) => T;
set(lens: Lens): <T, U>(replacer: U, obj: T) => T;

R.set source

import { always } from './always'
import { over } from './over'

export function set(
  lens, replacer, x
){
  if (arguments.length === 1) return (_v, _x) => set(
    lens, _v, _x
  )
  if (arguments.length === 2) return _x => set(
    lens, replacer, _x
  )

  return over(
    lens, always(replacer), x
  )
}

setter

setter(keyOrObject: string | object, value?: any): void

All Typescript definitions

setter(keyOrObject: string | object, value?: any): void;

shuffle

shuffle<T>(list: T[]): T[]

It returns a randomized copy of array.

All Typescript definitions

shuffle<T>(list: T[]): T[];

R.shuffle source

export function shuffle(arrayRaw){
  const array = arrayRaw.concat()
  let counter = array.length
  while (counter > 0){
    const index = Math.floor(Math.random() * counter)
    counter--
    const temp = array[ counter ]
    array[ counter ] = array[ index ]
    array[ index ] = temp
  }

  return array
}

Tests

import { range } from './range'
import { shuffle } from './shuffle'
import { uniq } from './uniq'

test('happy', () => {
  const list = range(0, 7)
  const result = range(0, 300).map(() => shuffle(list))
  const allUniq = uniq(result)
  expect(allUniq.length > 150).toBe(true)
})

slice

slice(from: number, to: number, list: string): string

It returns listOrString between from and to indexes.

const list = [0, 1, 2, 3, 4, 5]
const str = 'FOO_BAR'
const from = 1
const to = 4

const result = [
  R.slice(str, to, list),
  R.slice(from, to, list)
]
// => ['OO_', [1, 2, 3]]

Try the above R.slice example in Rambda REPL

All Typescript definitions

slice(from: number, to: number, list: string): string;
slice<T>(from: number, to: number, list: T[]): T[];
slice(from: number, to: number): {
  (list: string): string;
  <T>(list: T[]): T[];
};
slice(from: number): {
  (to: number, list: string): string;
  <T>(to: number, list: T[]): T[];
};

R.slice source

import { curry } from './curry'

function sliceFn(
  from, to, list
){
  return list.slice(from, to)
}

export const slice = curry(sliceFn)

Tests

import { slice } from './slice'

test('slice', () => {
  expect(slice(
    1, 3, [ 'a', 'b', 'c', 'd' ]
  )).toEqual([ 'b', 'c' ])
  expect(slice(
    1, Infinity, [ 'a', 'b', 'c', 'd' ]
  )).toEqual([ 'b', 'c', 'd' ])
  expect(slice(
    0, -1, [ 'a', 'b', 'c', 'd' ]
  )).toEqual([ 'a', 'b', 'c' ])
  expect(slice(
    -3, -1, [ 'a', 'b', 'c', 'd' ]
  )).toEqual([ 'b', 'c' ])
  expect(slice(
    0, 3, 'ramda'
  )).toEqual('ram')
})

sort

sort<T>(sortFn: (a: T, b: T) => number, list: ReadonlyArray<T>): T[]

It returns copy of list sorted by sortFn function.

const list = [
  {a: 2},
  {a: 3},
  {a: 1}
]
const sortFn = (x, y) => {
  return x.a > y.a ? 1 : -1
}

const result = R.sort(list, sortFn)
const expected = [
  {a: 1},
  {a: 2},
  {a: 3}
]
// => `result` is equal to `expected`

Try the above R.sort example in Rambda REPL

All Typescript definitions

sort<T>(sortFn: (a: T, b: T) => number, list: ReadonlyArray<T>): T[];
sort<T>(sortFn: (a: T, b: T) => number): (list: ReadonlyArray<T>) => T[];

R.sort source

export function sort(sortFn, list){
  if (arguments.length === 1) return _list => sort(sortFn, _list)

  const clone = list.slice()

  return clone.sort(sortFn)
}

Tests

import { sort } from './sort'

const fn = (a, b) => a > b ? 1 : -1

test('sort', () => {
  expect(sort((a, b) => a - b)([ 2, 3, 1 ])).toEqual([ 1, 2, 3 ])
})

test('it doesn\'t mutate', () => {
  const list = [ 'foo', 'bar', 'baz' ]

  expect(sort(fn, list)).toEqual([ 'bar', 'baz', 'foo' ])

  expect(list[ 0 ]).toBe('foo')
  expect(list[ 1 ]).toBe('bar')
  expect(list[ 2 ]).toBe('baz')
})

sortBy

sortBy<T>(sortFn: (a: T) => Ord, list: ReadonlyArray<T>): T[]

It returns copy of list sorted by sortFn function.

const list = [
  {a: 2},
  {a: 3},
  {a: 1}
]
const sortFn = x => x.a

const result = R.sortBy(list, sortFn)
const expected = [
  {a: 1},
  {a: 2},
  {a: 3}
]
// => `result` is equal to `expected`

Try the above R.sortBy example in Rambda REPL

All Typescript definitions

sortBy<T>(sortFn: (a: T) => Ord, list: ReadonlyArray<T>): T[];
sortBy(sortFn: (a: any) => Ord): <T>(list: ReadonlyArray<T>) => T[];

R.sortBy source

export function sortBy(sortFn, list){
  if (arguments.length === 1) return _list => sortBy(sortFn, _list)

  const clone = list.slice()

  return clone.sort((a, b) => {
    const aSortResult = sortFn(a)
    const bSortResult = sortFn(b)

    if (aSortResult === bSortResult) return 0

    return aSortResult < bSortResult ? -1 : 1
  })
}

Tests

import { compose } from './compose'
import { prop } from './prop'
import { sortBy } from './sortBy'
import { toLower } from './toLower'

test('happy', () => {
  const input = [ { a : 2 }, { a : 1 }, { a : 1 }, { a : 3 } ]
  const expected = [ { a : 1 }, { a : 1 }, { a : 2 }, { a : 3 } ]

  const result = sortBy(x => x.a)(input)
  expect(result).toEqual(expected)
})

test('with compose', () => {
  const alice = {
    name : 'ALICE',
    age  : 101,
  }
  const bob = {
    name : 'Bob',
    age  : -10,
  }
  const clara = {
    name : 'clara',
    age  : 314.159,
  }
  const people = [ clara, bob, alice ]
  const sortByNameCaseInsensitive = sortBy(compose(toLower, prop('name')))

  expect(sortByNameCaseInsensitive(people)).toEqual([ alice, bob, clara ])
})

Typescript test

import {sortBy} from 'rambda'

describe('sortBy', () => {
  it('happy', () => {
    interface Input {
      a: number,
    }

    function fn(x: Input): number {
      return x.a
    }

    const input: Input[] = [{a: 2}, {a: 1}, {a: 0}]
    const result = sortBy(fn, input)

    result // $ExpectType Input[]
    result[0].a // $ExpectType number
  })
})

1 failed Ramda.sortBy specs

💥 Reason for the failure: ramda works with array-like objects

var R = require('../../../../dist/rambda.js');
var eq = require('./shared/eq');

var albums = [
  {title: 'Art of the Fugue', artist: 'Glenn Gould', genre: 'Baroque'},
  {title: 'A Farewell to Kings', artist: 'Rush', genre: 'Rock'},
  {title: 'Timeout', artist: 'Dave Brubeck Quartet', genre: 'Jazz'},
  {title: 'Fly By Night', artist: 'Rush', genre: 'Rock'},
  {title: 'Goldberg Variations', artist: 'Daniel Barenboim', genre: 'Baroque'},
  {title: 'New World Symphony', artist: 'Leonard Bernstein', genre: 'Romantic'},
  {title: 'Romance with the Unseen', artist: 'Don Byron', genre: 'Jazz'},
  {title: 'Somewhere In Time', artist: 'Iron Maiden', genre: 'Metal'},
  {title: 'In Times of Desparation', artist: 'Danny Holt', genre: 'Modern'},
  {title: 'Evita', artist: 'Various', genre: 'Broadway'},
  {title: 'Five Leaves Left', artist: 'Nick Drake', genre: 'Folk'},
  {title: 'The Magic Flute', artist: 'John Eliot Gardiner', genre: 'Classical'}
];
describe('sortBy', function() {
  it('sorts array-like object', function() {
    var args = (function() { return arguments; }('c', 'a', 'b'));
    var result = R.sortBy(R.identity, args);
    eq(result[0], 'a');
    eq(result[1], 'b');
    eq(result[2], 'c');
  });
});

sortObject

sortObject<T>(predicate: SortObjectPredicate<T>, input: { [key: string]: T }): { [keyOutput: string]: T }

It returns a sorted version of input object.

const predicate = (propA, propB, valueA, valueB) => valueA > valueB ? -1 : 1

const result = R.sortObject(predicate, {a:1, b: 4, c: 2})
// => {b: 4, c: 2, a: 1}

Try the above R.sortObject example in Rambda REPL

All Typescript definitions

sortObject<T>(predicate: SortObjectPredicate<T>, input: { [key: string]: T }): { [keyOutput: string]: T };
sortObject<T>(predicate: SortObjectPredicate<T>): (input: { [key: string]: T }) => { [keyOutput: string]: T };

R.sortObject source

import { sort } from './sort'

export function sortObject(predicate, obj){
  if (arguments.length === 1){
    return _obj => sortObject(predicate, _obj)
  }
  const keys = Object.keys(obj)
  const sortedKeys = sort((a, b) => predicate(
    a, b, obj[ a ], obj[ b ]
  ), keys)
  const toReturn = {}
  sortedKeys.forEach(singleKey => {
    toReturn[ singleKey ] = obj[ singleKey ]
  })

  return toReturn
}

Tests

import { runTests } from 'helpers-fn'

import { equals } from './equals'
import { sortObject } from './sortObject'

const obj = {
  c : 1,
  a : 2,
  b : 3,
}
const predicateA = (
  propA, propB, valueA, valueB
) => propA > propB ? -1 : 1
const expectationA = [ 'c', 'b', 'a' ]
const predicateB = (
  propA, propB, valueA, valueB
) => propA < propB ? -1 : 1
const expectationB = [ 'a', 'b', 'c' ]
const predicateC = (
  propA, propB, valueA, valueB
) =>
  valueA > valueB ? -1 : 1
const expectationC = [ 'b', 'a', 'c' ]

const fn = ([ predicate, expectation ]) => {
  const result = sortObject(predicate, obj)
  const sortedKeys = Object.keys(result)
  const isSameObject = equals(obj, result)

  return isSameObject && equals(sortedKeys, expectation)
}

const testData = {
  label : 'foo',
  data  : [
    { ok : [ predicateA, expectationA ] },
    { ok : [ predicateB, expectationB ] },
    { ok : [ predicateC, expectationC ] },
  ],
  fn,
}

runTests(testData)

split

split(separator: string | RegExp): (str: string) => string[]

Curried version of String.prototype.split

const str = 'foo|bar|baz'
const separator = |'
const result = R.split(separator, str))
// => [ 'foo', 'bar', 'baz' ]

Try the above R.split example in Rambda REPL

All Typescript definitions

split(separator: string | RegExp): (str: string) => string[];
split(separator: string | RegExp, str: string): string[];

R.split source

export function split(separator, str){
  if (arguments.length === 1) return _str => split(separator, _str)

  return str.split(separator)
}

Tests

import { split } from './split'

test('split', () => {
  expect(split('|')('foo|bar|baz')).toEqual([ 'foo', 'bar', 'baz' ])

  expect(split('.', 'a.b.c.xyz.d')).toEqual([ 'a', 'b', 'c', 'xyz', 'd' ])
})

splitEvery

splitEvery<T>(sliceLength: number, listOrString: ReadonlyArray<T>): T[][]

It splits listOrString into slices of sliceLength.

const result = [
  R.splitEvery(2, [1, 2, 3]), 
  R.splitEvery(3, 'foobar') 
]

const expected = [
  [[1, 2], [3]],
  ['foo', 'bar']
]
// => `result` is equal to `expected`

Try the above R.splitEvery example in Rambda REPL

All Typescript definitions

splitEvery<T>(sliceLength: number, listOrString: ReadonlyArray<T>): T[][];
splitEvery(sliceLength: number, listOrString: string): string[];
splitEvery(sliceLength: number): {
  (listOrString: string): string[];
  <T>(listOrString: ReadonlyArray<T>): T[][];
};

R.splitEvery source

export function splitEvery(sliceLength, listOrString){
  if (arguments.length === 1){
    return _listOrString => splitEvery(sliceLength, _listOrString)
  }

  if (sliceLength < 1){
    throw new Error('First argument to splitEvery must be a positive integer')
  }

  const willReturn = []
  let counter = 0

  while (counter < listOrString.length){
    willReturn.push(listOrString.slice(counter, counter += sliceLength))
  }

  return willReturn
}

Tests

import { splitEvery } from './splitEvery'

test('happy', () => {
  expect(splitEvery(3, [ 1, 2, 3, 4, 5, 6, 7 ])).toEqual([
    [ 1, 2, 3 ],
    [ 4, 5, 6 ],
    [ 7 ],
  ])

  expect(splitEvery(3)('foobarbaz')).toEqual([ 'foo', 'bar', 'baz' ])
})

test('with bad input', () => {
  expect(() =>
    expect(splitEvery(0)('foo')).toEqual([ 'f', 'o', 'o' ])).toThrow('First argument to splitEvery must be a positive integer')
})

startsWith

startsWith(target: string, str: string): boolean

Curried version of String.prototype.startsWith

const str = 'foo-bar'

const result = [
  R.startsWith('foo', str),
  R.startsWith('bar', str)
]
// => [true, false]

Try the above R.startsWith example in Rambda REPL

All Typescript definitions

startsWith(target: string, str: string): boolean;
startsWith(target: string): (str: string) => boolean;

R.startsWith source

export function startsWith(target, str){
  if (arguments.length === 1) return _str => startsWith(target, _str)

  return str.startsWith(target)
}

Tests

import { startsWith } from './startsWith'

test('true', () => {
  const result = startsWith('foo', 'foo-bar')

  expect(result).toBeTrue()
})

test('false', () => {
  const result = startsWith('baz')('foo-bar')

  expect(result).toBeFalse()
})

4 failed Ramda.startsWith specs

💥 Reason for the failure: rambda doesn't support arrays

var R = require('../../../../dist/rambda.js');
var eq = require('./shared/eq');

describe('startsWith', function() {
  it('should return true when an array starts with the provided value', function() {
    eq(R.startsWith(['a'], ['a', 'b', 'c']), true);
  });
  it('should return true when an array starts with the provided values', function() {
    eq(R.startsWith(['a', 'b'], ['a', 'b', 'c']), true);
  });
  it('should return false when an array does not start with the provided value', function() {
    eq(R.startsWith(['b'], ['a', 'b', 'c']), false);
  });
  it('should return false when an array does not start with the provided values', function() {
    eq(R.startsWith(['b', 'c'], ['a', 'b', 'c']), false);
  });
});

subtract

subtract(x: number, y: number): number

Curried version of x - y

const x = 3
const y = 1

R.subtract(x, y) 
// => 2

Try the above R.subtract example in Rambda REPL

All Typescript definitions

subtract(x: number, y: number): number;
subtract(x: number): (y: number) => number;

R.subtract source

export function subtract(a, b){
  if (arguments.length === 1) return _b => subtract(a, _b)

  return a - b
}

Tests

import { subtract } from './subtract'

test('happy', () => {
  expect(subtract(2, 1)).toEqual(1)
  expect(subtract(2)(1)).toEqual(1)
})

sum

sum(list: ReadonlyArray<number>): number

R.sum([1, 2, 3, 4, 5]) 
// => 15

Try the above R.sum example in Rambda REPL

All Typescript definitions

sum(list: ReadonlyArray<number>): number;

R.sum source

export function sum(list){
  return list.reduce((prev, current) => prev + current, 0)
}

Tests

import { sum } from './sum'

test('happy', () => {
  expect(sum([ 1, 2, 3, 4, 5 ])).toBe(15)
})

switcher

switcher<T>(valueToMatch: any): Switchem<T>

Edited fork of Switchem library.

const valueToMatch = {foo: 1}

const result = R.switcher(valueToMatch)
  .is('baz', 'is baz')
  .is(x => typeof x === 'boolean', 'is boolean')
  .is({foo: 1}, 'Property foo is 1')
  .default('is bar')

// => 'Property foo is 1'

Try the above R.switcher example in Rambda REPL

All Typescript definitions

switcher<T>(valueToMatch: any): Switchem<T>;

R.switcher source

import { equals } from './equals'

const NO_MATCH_FOUND = Symbol ? Symbol('NO_MATCH_FOUND') : undefined

const getMatchingKeyValuePair = (
  cases, testValue, defaultValue
) => {
  let iterationValue

  for (let index = 0; index < cases.length; index++){
    iterationValue = cases[ index ].test(testValue)

    if (iterationValue !== NO_MATCH_FOUND){
      return iterationValue
    }
  }

  return defaultValue
}

const isEqual = (testValue, matchValue) => {
  const willReturn =
    typeof testValue === 'function' ?
      testValue(matchValue) :
      equals(testValue, matchValue)

  return willReturn
}

const is = (testValue, matchResult = true) => ({
  key  : testValue,
  test : matchValue =>
    isEqual(testValue, matchValue) ? matchResult : NO_MATCH_FOUND,
})

class Switchem{
  constructor(
    defaultValue, cases, willMatch
  ){
    if (
      defaultValue !== undefined &&
      cases === undefined &&
      willMatch === undefined
    ){
      this.cases = []
      this.defaultValue = undefined
      this.willMatch = defaultValue
    } else {
      this.cases = cases
      this.defaultValue = defaultValue
      this.willMatch = willMatch
    }

    return this
  }

  default(defaultValue){
    const holder = new Switchem(
      defaultValue, this.cases, this.willMatch
    )

    return holder.match(this.willMatch)
  }

  is(testValue, matchResult){
    return new Switchem(
      this.defaultValue,
      [ ...this.cases, is(testValue, matchResult) ],
      this.willMatch
    )
  }

  match(matchValue){
    return getMatchingKeyValuePair(
      this.cases, matchValue, this.defaultValue
    )
  }
}

export function switcher(input){
  return new Switchem(input)
}

Tests

import { add } from './add'
import { delay } from './delay'
import { identity } from './identity'
import { switcher } from './switcher'
import { tap } from './tap'
import { trim } from './trim'
import { type } from './type'

test('accept function as answers', () => {
  const fn = switcher('foo').is('bar', tap)
    .is('foo', add(1))
    .default(trim)

  expect(fn(2)).toEqual(3)
})

test('with boolean tuple', () => {
  const a = true
  const b = false
  const result = switcher([ a, b ])
    .is([ false, false ], '0')
    .is([ false, true ], '1')
    .is([ true, true ], '2')
    .default('3')

  expect(result).toEqual('3')
})

test('with boolean tuple - second test', () => {
  const a = true
  const b = true
  const result = switcher([ a, b ])
    .is([ false, false ], '0')
    .is([ false, true ], '1')
    .is([ true, true ], '2')
    .default('3')

  expect(result).toEqual('2')
})

test('works with objects as arguments', () => {
  const result = switcher({ a : 1 })
    .is({ a : 1 }, 'it is bar')
    .is('baz', 'it is baz')
    .default('it is default')

  expect(result).toEqual('it is bar')
})

const switchFn = input =>
  switcher(input)
    .is({ a : 1 }, 'it is bar')
    .is(x => x.length && x.length === 7, 'has length of 7')
    .is('baz', 'it is baz')
    .default('it is default')

test('hits default of no matches', () => {
  expect(switchFn(1)).toEqual('it is default')
})

test('works with function as condition', () => {
  expect(switchFn([ 0, 1, 2, 3, 4, 5, 6 ])).toEqual('has length of 7')
})

test('works with string as condition', () => {
  expect(switchFn('baz')).toEqual('it is baz')
})

test('works with functions as condition result', () => {
  const input = 'foo'
  const result = switcher(input).is('foo', delay)
    .default(identity)

  expect(type(result())).toEqual('Promise')
})

symmetricDifference

symmetricDifference<T>(x: ReadonlyArray<T>, y: ReadonlyArray<T>): T[]

It returns a merged list of x and y with all equal elements removed.

const x = [ 1, 2, 3, 4 ]
const y = [ 3, 4, 5, 6 ]

const result = symmetricDifference(x, y)
// => [ 1, 2, 5, 6 ]

Try the above R.symmetricDifference example in Rambda REPL

All Typescript definitions

symmetricDifference<T>(x: ReadonlyArray<T>, y: ReadonlyArray<T>): T[];
symmetricDifference<T>(x: ReadonlyArray<T>): <T>(y: ReadonlyArray<T>) => T[];

R.symmetricDifference source

import { concat } from './concat'
import { filter } from './filter'
import { includes } from './includes'

export function symmetricDifference(x, y){
  if (arguments.length === 1){
    return _y => symmetricDifference(x, _y)
  }

  return concat(filter(value => !includes(value, y), x),
    filter(value => !includes(value, x), y))
}

Tests

import { symmetricDifference } from './symmetricDifference'

test('symmetricDifference', () => {
  const list1 = [ 1, 2, 3, 4 ]
  const list2 = [ 3, 4, 5, 6 ]
  expect(symmetricDifference(list1)(list2)).toEqual([ 1, 2, 5, 6 ])

  expect(symmetricDifference([], [])).toEqual([])
})

test('symmetricDifference with objects', () => {
  const list1 = [ { id : 1 }, { id : 2 }, { id : 3 }, { id : 4 } ]
  const list2 = [ { id : 3 }, { id : 4 }, { id : 5 }, { id : 6 } ]
  expect(symmetricDifference(list1)(list2)).toEqual([
    { id : 1 },
    { id : 2 },
    { id : 5 },
    { id : 6 },
  ])
})

T

T(): boolean

R.T() 
// => true

Try the above R.T example in Rambda REPL

All Typescript definitions

T(): boolean;

R.T source

export function T(){
  return true
}

tail

tail<T>(listOrString: ReadonlyArray<T>): T[]

It returns all but the first element of listOrString.

const result = [
  R.tail([1, 2, 3]),  
  R.tail('foo') 
]
// => [[2, 3], 'oo']

Try the above R.tail example in Rambda REPL

All Typescript definitions

tail<T>(listOrString: ReadonlyArray<T>): T[];
tail(listOrString: string): string;

R.tail source

import { drop } from './drop'

export function tail(listOrString){
  return drop(1, listOrString)
}

Tests

import { tail } from './tail'

test('tail', () => {
  expect(tail([ 1, 2, 3 ])).toEqual([ 2, 3 ])
  expect(tail([ 1, 2 ])).toEqual([ 2 ])
  expect(tail([ 1 ])).toEqual([])
  expect(tail([])).toEqual([])

  expect(tail('abc')).toEqual('bc')
  expect(tail('ab')).toEqual('b')
  expect(tail('a')).toEqual('')
  expect(tail('')).toEqual('')
})

take

take<T>(howMany: number, listOrString: ReadonlyArray<T>): T[]

It returns the first howMany elements of listOrString.

const howMany = 2

const result = [
  R.take(howMany, [1, 2, 3]),
  R.take(howMany, 'foobar'),
]
// => [[1, 2], 'fo']

Try the above R.take example in Rambda REPL

All Typescript definitions

take<T>(howMany: number, listOrString: ReadonlyArray<T>): T[];
take(howMany: number, listOrString: string): string;
take<T>(howMany: number): {
  (listOrString: string): string;
  (listOrString: ReadonlyArray<T>): T[];
};

R.take source

import baseSlice from './_internals/baseSlice'

export function take(howMany, listOrString){
  if (arguments.length === 1)
    return _listOrString => take(howMany, _listOrString)
  if (howMany < 0) return listOrString.slice()
  if (typeof listOrString === 'string') return listOrString.slice(0, howMany)

  return baseSlice(
    listOrString, 0, howMany
  )
}

Tests

import { take } from './take'

test('happy', () => {
  const arr = [ 'foo', 'bar', 'baz' ]

  expect(take(1, arr)).toEqual([ 'foo' ])

  expect(arr).toEqual([ 'foo', 'bar', 'baz' ])

  expect(take(2)([ 'foo', 'bar', 'baz' ])).toEqual([ 'foo', 'bar' ])
  expect(take(3, [ 'foo', 'bar', 'baz' ])).toEqual([ 'foo', 'bar', 'baz' ])
  expect(take(4, [ 'foo', 'bar', 'baz' ])).toEqual([ 'foo', 'bar', 'baz' ])
  expect(take(3)('rambda')).toEqual('ram')
})

test('with negative index', () => {
  expect(take(-1, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
  expect(take(-Infinity, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
})

test('with zero index', () => {
  expect(take(0, [ 1, 2, 3 ])).toEqual([])
})

3 failed Ramda.take specs

💥 Reason for the failure: rambda doesn't have 'R.into` method

var assert = require('assert');
var sinon = require('sinon');

var R = require('../../../../dist/rambda.js');
var eq = require('./shared/eq');
describe('take', function() {
  it('handles zero correctly (#1224)', function() {
    eq(R.into([], R.take(0), [1, 2, 3]), []);
  });
  it('steps correct number of times', function() {
    var spy = sinon.spy();
    R.into([], R.compose(R.map(spy), R.take(2)), [1, 2, 3]);
    sinon.assert.calledTwice(spy);
  });
  it('transducer called for every member of list if `n` is < 0', function() {
    var spy = sinon.spy();
    R.into([], R.compose(R.map(spy), R.take(-1)), [1, 2, 3]);
    sinon.assert.calledThrice(spy);
  });
});

takeLast

takeLast<T>(howMany: number, listOrString: ReadonlyArray<T>): T[]

It returns the last howMany elements of listOrString.

const howMany = 2

const result = [
  R.takeLast(howMany, [1, 2, 3]),
  R.takeLast(howMany, 'foobar'),
]
// => [[2, 3], 'ar']

Try the above R.takeLast example in Rambda REPL

All Typescript definitions

takeLast<T>(howMany: number, listOrString: ReadonlyArray<T>): T[];
takeLast(howMany: number, listOrString: string): string;
takeLast<T>(howMany: number): {
  (listOrString: string): string;
  (listOrString: ReadonlyArray<T>): T[];
};

R.takeLast source

import baseSlice from './_internals/baseSlice'

export function takeLast(howMany, listOrString){
  if (arguments.length === 1)
    return _listOrString => takeLast(howMany, _listOrString)

  const len = listOrString.length
  if (howMany < 0) return listOrString.slice()
  let numValue = howMany > len ? len : howMany

  if (typeof listOrString === 'string')
    return listOrString.slice(len - numValue)

  numValue = len - numValue

  return baseSlice(
    listOrString, numValue, len
  )
}

Tests

import { takeLast } from './takeLast'

test('with arrays', () => {
  expect(takeLast(1, [ 'foo', 'bar', 'baz' ])).toEqual([ 'baz' ])

  expect(takeLast(2)([ 'foo', 'bar', 'baz' ])).toEqual([ 'bar', 'baz' ])

  expect(takeLast(3, [ 'foo', 'bar', 'baz' ])).toEqual([ 'foo', 'bar', 'baz' ])

  expect(takeLast(4, [ 'foo', 'bar', 'baz' ])).toEqual([ 'foo', 'bar', 'baz' ])

  expect(takeLast(10, [ 'foo', 'bar', 'baz' ])).toEqual([ 'foo', 'bar', 'baz' ])
})

test('with strings', () => {
  expect(takeLast(3, 'rambda')).toEqual('bda')

  expect(takeLast(7, 'rambda')).toEqual('rambda')
})

test('with negative index', () => {
  expect(takeLast(-1, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
  expect(takeLast(-Infinity, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
})

tap

tap<T>(fn: (a: T) => any, x: T): T

It applies function fn to input x and returns x.

One use case is debuging in the middle of R.compose.

const list = [1, 2, 3]

R.compose(
  R.map(x => x * 2)
  R.tap(console.log),
  R.filter(x => x > 1)
)(list)
// => `2` and `3` will be logged

Try the above R.tap example in Rambda REPL

All Typescript definitions

tap<T>(fn: (a: T) => any, x: T): T;
tap<T>(fn: (a: T) => any): (x: T) => T;

R.tap source

export function tap(fn, x){
  if (arguments.length === 1) return _x => tap(fn, _x)

  fn(x)

  return x
}

Tests

import { tap } from './tap'

test('tap', () => {
  let a = 1
  const sayX = x => a = x

  expect(tap(sayX, 100)).toEqual(100)
  expect(tap(sayX)(100)).toEqual(100)
  expect(a).toEqual(100)
})

2 failed Ramda.tap specs

💥 Reason for the failure: ramda can act as a transducer

var R = require('../../../../dist/rambda.js');
var eq = require('./shared/eq');
var listXf = require('./helpers/listXf');
var _curry2 = require('rambda/internal/_curry2');

describe('tap', function() {
  var pushToList = _curry2(function(lst, x) { lst.push(x); });
  it('can act as a transducer', function() {
    var sideEffect = [];
    var numbers = [1,2,3,4,5];
    var xf = R.compose(R.map(R.identity), R.tap(pushToList(sideEffect)));
    eq(R.into([], xf, numbers), numbers);
    eq(sideEffect, numbers);
  });
  it('dispatches to transformer objects', function() {
    var sideEffect = [];
    var pushToSideEffect = pushToList(sideEffect);
    eq(R.tap(pushToSideEffect, listXf), {
      f: pushToSideEffect,
      xf: listXf
    });
  });
});

tapAsync

tapAsync<T>(fn: Func<any> | Promise<any>, input: T): T

Asynchronous version of R.tap.

All Typescript definitions

tapAsync<T>(fn: Func<any> | Promise<any>, input: T): T;
tapAsync<T>(fn: Func<any> | Promise<any>): (input: T) => T;

R.tapAsync source

import { isPromise } from './isPromise'

export function tapAsync(fn, input){
  if (arguments.length === 1){
    return inputHolder => tapAsync(fn, inputHolder)
  }
  if (isPromise(fn) === true){
    return new Promise((resolve, reject) => {
      fn(input)
        .then(() => {
          resolve(input)
        })
        .catch(reject)
    })
  }
  fn(input)

  return input
}

Tests

import { delay } from './delay'
import { tapAsync } from './tapAsync'

test('', async () => {
  const result = await tapAsync(delay)(1)
  expect(result).toEqual(1)
})

template

template(inputWithTags: string, templateArguments: object): string

It generages a new string from inputWithTags by replacing all {{x}} occurances with values provided by templateArguments.

const inputWithTags = 'foo is {{bar}} even {{a}} more'
const templateArguments = {"bar":"BAR", a: 1}

const result = R.template(inputWithTags, templateArguments)
const expected = 'foo is BAR even 1 more'
// => `result` is equal to `expected`

Try the above R.template example in Rambda REPL

All Typescript definitions

template(inputWithTags: string, templateArguments: object): string;
template(inputWithTags: string): (templateArguments: object) => string;

R.template source

const escapeSpecialCharacters = s =>
  s.replace(/[-\/\\^$*+?.()|[\]{}]/g, '\\{{rambdaSource}}')

const getOccurances = input => input.match(/{{\s*.+?\s*}}/g)

const getOccuranceProp = occurance => occurance.replace(/{{\s*|\s*}}/g, '')

const replace = ({ inputHolder, prop, replacer }) =>
  inputHolder.replace(new RegExp(`{{\\s*${ escapeSpecialCharacters(prop) }\\s*}}`),
    replacer)

export function template(input, templateInput){
  if (arguments.length === 1){
    return templateInputHolder => template(input, templateInputHolder)
  }

  const occurances = getOccurances(input)
  if (occurances === null) return input
  let inputHolder = input
  for (const occurance of occurances){
    const prop = getOccuranceProp(occurance)

    try {
      const replacer = new Function('templateInput',
        `with(templateInput) { return ${ prop } }`)(templateInput)

      inputHolder = replace({
        inputHolder,
        prop,
        replacer,
      })
    } catch (e){}
  }

  return inputHolder
}

Tests

import { template } from './template'

test('within bracets', () => {
  const input = 'foo is { {{bar}} } even {{a}} more'
  const templateInput = {
    bar : 'BAR',
    a   : 1,
  }

  const result = template(input, templateInput)
  const expectedResult = 'foo is { BAR } even 1 more'

  expect(result).toEqual(expectedResult)
})

test('happy', () => {
  const input = 'foo is {{bar}} even {{a}} more'
  const templateInput = {
    bar : 'BAR',
    a   : 1,
  }

  const result = template(input, templateInput)
  const expectedResult = 'foo is BAR even 1 more'

  expect(result).toEqual(expectedResult)
})

test('no interpolation + curry', () => {
  const input = 'foo is bar even more'
  const templateInput = { bar : 'BAR' }

  const result = template(input)(templateInput)
  const expectedResult = 'foo is bar even more'

  expect(result).toEqual(expectedResult)
})

test('with missing template input', () => {
  const input = 'foo is {{bar}} even {{a}} more'
  const templateInput = {
    baz : 'BAR',
    a   : 1,
  }

  const result = template(input, templateInput)
  const expectedResult = 'foo is {{bar}} even 1 more'

  expect(result).toEqual(expectedResult)
})

test('with arbitrary expression', () => {
  const input = '1 + 2 = {{ 1 + 2 }}'
  const templateInput = {}

  const expectedResult = '1 + 2 = 3'
  const result = template(input, templateInput)

  expect(result).toEqual(expectedResult)
})

test

test(regExpression: RegExp): (str: string) => boolean

It determines whether str matches regExpression.

R.test(/^f/, 'foo')
// => true

Try the above R.test example in Rambda REPL

All Typescript definitions

test(regExpression: RegExp): (str: string) => boolean;
test(regExpression: RegExp, str: string): boolean;

R.test source

export function test(pattern, str){
  if (arguments.length === 1) return _str => test(pattern, _str)

  if (typeof pattern === 'string'){
    throw new TypeError(`‘test’ requires a value of type RegExp as its first argument; received "${ pattern }"`)
  }

  return str.search(pattern) !== -1
}

Tests

import { test as testMethod } from './test'

test('happy', () => {
  expect(testMethod(/^x/, 'xyz')).toBeTrue()

  expect(testMethod(/^y/)('xyz')).toBeFalse()
})

test('throws if first argument is not regex', () => {
  expect(() => testMethod('foo', 'bar')).toThrow('‘test’ requires a value of type RegExp as its first argument; received "foo"')
})

throttle

throttle<T>(fn: T, ms: number): (input: T) => T

It creates a throttled function that invokes fn maximum once for a period of milliseconds.

let counter = 0
const inc = () => {
  counter++
}

const throttledInc = R.throttle(inc, 800)

const result = async () => {
  throttledInc()
  await R.delay(500)
  throttledInc()

  return counter
}
// `result` resolves to `1`

Try the above R.throttle example in Rambda REPL

All Typescript definitions

throttle<T>(fn: T, ms: number): (input: T) => T;

R.throttle source

export function throttle(fn, ms){
  let wait = false

  return function (...input){
    if (!wait){
      fn.apply(null, input)
      wait = true
      setTimeout(() => {
        wait = false
      }, ms)
    }
  }
}

Tests

import { delay } from './delay'
import { throttle } from './throttle'

test('', async () => {
  let counter = 0
  let aHolder
  let bHolder

  const inc = (a, b) => {
    aHolder = a
    bHolder = b
    counter++
  }

  const incWrapped = throttle(inc, 1000)

  incWrapped(1, 2)

  await delay(500)

  incWrapped(2, 3)
  incWrapped(3, 4)

  expect(counter).toBe(1)
  expect(aHolder).toBe(1)
  expect(bHolder).toBe(2)

  await delay(1000)

  incWrapped(5, 6)

  expect(counter).toBe(2)
  expect(aHolder).toBe(5)
  expect(bHolder).toBe(6)
})

times

times<T>(fn: (i: number) => T, howMany: number): T[]

It returns the result of applying function fn over members of range array.

The range array includes numbers between 0 and howMany(exclusive).

const fn = x => x * 2
const howMany = 5

R.times(fn, howMany)
//=> [0, 2, 4, 6, 8]

Try the above R.times example in Rambda REPL

All Typescript definitions

times<T>(fn: (i: number) => T, howMany: number): T[];
times<T>(fn: (i: number) => T): (howMany: number) => T[];

R.times source

import { map } from './map'
import { range } from './range'

export function times(fn, howMany){
  if (arguments.length === 1) return _howMany => times(fn, _howMany)
  if (!Number.isInteger(howMany) || howMany < 0){
    throw new RangeError('n must be an integer')
  }

  return map(fn, range(0, howMany))
}

Tests

import assert from 'assert'

import { identity } from './identity'
import { times } from './times'

test('happy', () => {
  const result = times(identity, 5)

  expect(result).toEqual([ 0, 1, 2, 3, 4 ])
})

test('with bad input', () => {
  assert.throws(() => {
    times(3)('cheers!')
  }, RangeError)
  assert.throws(() => {
    times(identity, -1)
  }, RangeError)
})

test('curry', () => {
  const result = times(identity)(5)

  expect(result).toEqual([ 0, 1, 2, 3, 4 ])
})

toDecimal

toDecimal(num: number, charsAfterDecimalPoint?: number): number

R.toDecimal(2.45464,2) // => 2.45

Try the above R.toDecimal example in Rambda REPL

All Typescript definitions

toDecimal(num: number, charsAfterDecimalPoint?: number): number;

R.toDecimal source

export function toDecimal(number, charsAfterDecimalPoint = 2){
  return Number(parseFloat(String(number)).toFixed(charsAfterDecimalPoint))
}

Tests

import { toDecimal } from './toDecimal'

test('', () => {
  expect(toDecimal(2.2789, 1)).toBe(2.3)
  expect(toDecimal(2.2789, 3)).toBe(2.279)
  expect(toDecimal(2.2789)).toBe(2.28)
  expect(toDecimal(2.45464)).toBe(2.45)
})

toLower

toLower(str: string): string

R.toLower('FOO')
// => 'foo'

Try the above R.toLower example in Rambda REPL

All Typescript definitions

toLower(str: string): string;

R.toLower source

export function toLower(str){
  return str.toLowerCase()
}

Tests

import { toLower } from './toLower'

test('toLower', () => {
  expect(toLower('FOO|BAR|BAZ')).toEqual('foo|bar|baz')
})

toPairs

toPairs<S>(obj: { [k: string]: S } | { [k: number]: S }): [string, S][]

It transforms an object to a list.

const list = {
  a : 1,
  b : 2,
  c : [ 3, 4 ],
}
const expected = [ [ 'a', 1 ], [ 'b', 2 ], [ 'c', [ 3, 4 ] ] ]

const result = R.toPairs(list)
// => `result` is equal to `expected`

Try the above R.toPairs example in Rambda REPL

All Typescript definitions

toPairs<S>(obj: { [k: string]: S } | { [k: number]: S }): [string, S][];

R.toPairs source

export function toPairs(obj){
  return Object.entries(obj)
}

Tests

import { toPairs } from './toPairs'

const obj = {
  a : 1,
  b : 2,
  c : [ 3, 4 ],
}
const expected = [
  [ 'a', 1 ],
  [ 'b', 2 ],
  [ 'c', [ 3, 4 ] ],
]

test('happy', () => {
  expect(toPairs(obj)).toEqual(expected)
})

toString

toString<T>(x: T): string

R.toString([1, 2]) 
// => '1,2'

Try the above R.toString example in Rambda REPL

All Typescript definitions

toString<T>(x: T): string;

R.toString source

export function toString(val){
  return val.toString()
}

Tests

import { toString } from './toString'

test('happy', () => {
  expect(toString([ 1, 2, 3 ])).toEqual('1,2,3')
})

toUpper

toUpper(str: string): string

R.toUpper('foo')
// => 'FOO'

Try the above R.toUpper example in Rambda REPL

All Typescript definitions

toUpper(str: string): string;

R.toUpper source

export function toUpper(str){
  return str.toUpperCase()
}

Tests

import { toUpper } from './toUpper'

test('toUpper', () => {
  expect(toUpper('foo|bar|baz')).toEqual('FOO|BAR|BAZ')
})

transpose

transpose<T>(list: T[][]): T[][]

const list = [[10, 11], [20], [], [30, 31, 32]]
const expected = [[10, 20, 30], [11, 31], [32]]

const result = R.transpose(list)
// => `result` is equal to `expected`

Try the above R.transpose example in Rambda REPL

All Typescript definitions

transpose<T>(list: T[][]): T[][];

R.transpose source

import { _isArray } from './_internals/_isArray'

export function transpose(array){
  return array.reduce((acc, el) => {
    el.forEach((nestedEl, i) =>
      _isArray(acc[ i ]) ? acc[ i ].push(nestedEl) : acc.push([ nestedEl ]))

    return acc
  }, [])
}

Tests

import { transpose } from './transpose'

test('happy', () => {
  const input = [
    [ 'a', 1 ],
    [ 'b', 2 ],
    [ 'c', 3 ],
  ]

  expect(transpose(input)).toEqual([
    [ 'a', 'b', 'c' ],
    [ 1, 2, 3 ],
  ])
})

test('when rows are shorter', () => {
  const actual = transpose([ [ 10, 11 ], [ 20 ], [], [ 30, 31, 32 ] ])
  const expected = [ [ 10, 20, 30 ], [ 11, 31 ], [ 32 ] ]
  expect(actual).toEqual(expected)
})

test('with empty array', () => {
  expect(transpose([])).toEqual([])
})

test('array with falsy values', () => {
  const actual = transpose([
    [ true, false, undefined, null ],
    [ null, undefined, false, true ],
  ])
  const expected = [
    [ true, null ],
    [ false, undefined ],
    [ undefined, false ],
    [ null, true ],
  ]
  expect(actual).toEqual(expected)
})

trim

trim(str: string): string

R.trim('  foo  ') 
// => 'foo'

Try the above R.trim example in Rambda REPL

All Typescript definitions

trim(str: string): string;

R.trim source

export function trim(str){
  return str.trim()
}

Tests

import { trim } from './trim'

test('trim', () => {
  expect(trim(' foo ')).toEqual('foo')
})

1 failed Ramda.trim specs

💥 Reason for the failure: ramda trims all ES5 whitespace

var R = require('../../../../dist/rambda.js');
var eq = require('./shared/eq');

describe('trim', function() {
  var test = '\x09\x0A\x0B\x0C\x0D\x20\xA0\u1680\u180E\u2000\u2001\u2002\u2003\u2004\u2005\u2006\u2007\u2008\u2009\u200A\u202F\u205F\u3000\u2028\u2029\uFEFFHello, World!\x09\x0A\x0B\x0C\x0D\x20\xA0\u1680\u180E\u2000\u2001\u2002\u2003\u2004\u2005\u2006\u2007\u2008\u2009\u200A\u202F\u205F\u3000\u2028\u2029\uFEFF';
  it('trims all ES5 whitespace', function() {
    eq(R.trim(test), 'Hello, World!');
    eq(R.trim(test).length, 13);
  });
  if (typeof String.prototype.trim !== 'function') {
    it('falls back to a shim if String.prototype.trim is not present', function() {
      eq(R.trim('   xyz  '), 'xyz');
      eq(R.trim(test), 'Hello, World!');
      eq(R.trim(test).length, 13);
      eq(R.trim('\u200b'), '\u200b');
      eq(R.trim('\u200b').length, 1);
    });
  }
});

tryCatch

tryCatch<T>(
  fn: any,
  fallback: any
): (...inputs: any[]) => Async<T> | T

All Typescript definitions

tryCatch<T>(
  fn: any,
  fallback: any
): (...inputs: any[]) => Async<T> | T;

type

type(x: any): "Object" | "Number" | "Boolean" | "String" | "Null" | "Array" | "Function" | "Undefined" | "Async" | "Promise" | "RegExp" | "NaN"

It accepts any input and it returns its type.

R.type(() => {}) // => 'Function'
R.type(async () => {}) // => 'Async'
R.type([]) // => 'Array'
R.type({}) // => 'Object'
R.type('foo') // => 'String'
R.type(1) // => 'Number'
R.type(true) // => 'Boolean'
R.type(null) // => 'Null'
R.type(/[A-z]/) // => 'RegExp'
R.type('foo'*1) // => 'NaN'

const delay = ms => new Promise(resolve => {
  setTimeout(function () {
    resolve()
  }, ms)
})
R.type(delay) // => 'Promise'

Try the above R.type example in Rambda REPL

All Typescript definitions

type(x: any): "Object" | "Number" | "Boolean" | "String" | "Null" | "Array" | "Function" | "Undefined" | "Async" | "Promise" | "RegExp" | "NaN";

R.type source

import { _isArray } from './_internals/_isArray'

export function type(input){
  const typeOf = typeof input

  if (input === null){
    return 'Null'
  } else if (input === undefined){
    return 'Undefined'
  } else if (typeOf === 'boolean'){
    return 'Boolean'
  } else if (typeOf === 'number'){
    return Number.isNaN(input) ? 'NaN' : 'Number'
  } else if (typeOf === 'string'){
    return 'String'
  } else if (_isArray(input)){
    return 'Array'
  } else if (input instanceof RegExp){
    return 'RegExp'
  }

  const asStr = input && input.toString ? input.toString() : ''

  if ([ 'true', 'false' ].includes(asStr)) return 'Boolean'
  if (!Number.isNaN(Number(asStr))) return 'Number'
  if (asStr.startsWith('async')) return 'Async'
  if (asStr === '[object Promise]') return 'Promise'
  if (typeOf === 'function') return 'Function'
  if (input instanceof String) return 'String'

  return 'Object'
}

Tests

import { type as ramdaType } from 'ramda'

import { type } from './type'

test('with simple promise', () => {
  expect(type(Promise.resolve(1))).toBe('Promise')
})

test('with new Boolean', () => {
  expect(type(new Boolean(true))).toBe('Boolean')
})

test('with new String', () => {
  expect(type(new String('I am a String object'))).toEqual('String')
})

test('with new Number', () => {
  expect(type(new Number(1))).toBe('Number')
})

test('with new promise', () => {
  const delay = ms =>
    new Promise(resolve => {
      setTimeout(() => {
        resolve(ms + 110)
      }, ms)
    })

  expect(type(delay(10))).toEqual('Promise')
})

test('async function', () => {
  expect(type(async () => {})).toEqual('Async')
})

test('async arrow', () => {
  const asyncArrow = async () => {}
  expect(type(asyncArrow)).toBe('Async')
})

test('function', () => {
  const fn1 = () => {}
  const fn2 = function (){}

  function fn3(){}

  ;[ () => {}, fn1, fn2, fn3 ].map(val => {
    expect(type(val)).toEqual('Function')
  })
})

test('object', () => {
  expect(type({})).toEqual('Object')
})

test('number', () => {
  expect(type(1)).toEqual('Number')
})

test('boolean', () => {
  expect(type(false)).toEqual('Boolean')
})

test('string', () => {
  expect(type('foo')).toEqual('String')
})

test('null', () => {
  expect(type(null)).toEqual('Null')
})

test('array', () => {
  expect(type([])).toEqual('Array')
  expect(type([ 1, 2, 3 ])).toEqual('Array')
})

test('regex', () => {
  expect(type(/\s/g)).toEqual('RegExp')
})

test('undefined', () => {
  expect(type(undefined)).toEqual('Undefined')
})

test('not a number', () => {
  expect(type(Number('s'))).toBe('NaN')
})

test('function inside object 1', () => {
  const obj = {
    f(){
      return 4
    },
  }

  expect(type(obj.f)).toBe('Function')
  expect(ramdaType(obj.f)).toBe('Function')
})

test('function inside object 2', () => {
  const name = 'f'
  const obj = {
    [ name ](){
      return 4
    },
  }
  expect(type(obj.f)).toBe('Function')
  expect(ramdaType(obj.f)).toBe('Function')
})

1 failed Ramda.type specs

💥 Reason for the failure: ramda returns 'Number' type to NaN input, while rambda returns 'NaN'

var R = require('../../../../dist/rambda.js');
var eq = require('./shared/eq');

describe('type', function() {
  // it('"Arguments" if given an arguments object', function() {
  //   var args = (function() { return arguments; }());
  //   eq(R.type(args), 'Arguments');
  // });
  it('"Number" if given the NaN value', function() {
    eq(R.type(NaN), 'Number');
  });
});

uniq

uniq<T>(list: ReadonlyArray<T>): T[]

It returns a new array containing only one copy of each element of list.

const list = [1, 1, {a: 1}, {a: 2}, {a:1}]

R.uniq(list)
// => [1, {a: 1}, {a: 2}]

Try the above R.uniq example in Rambda REPL

All Typescript definitions

uniq<T>(list: ReadonlyArray<T>): T[];

R.uniq source

import { includes } from './includes'

export function uniq(list){
  let index = -1
  const willReturn = []

  while (++index < list.length){
    const value = list[ index ]

    if (!includes(value, willReturn)){
      willReturn.push(value)
    }
  }

  return willReturn
}

Tests

import { uniq } from './uniq'

test('uniq', () => {
  expect(uniq([ 1, 2, 3, 3, 3, 1, 2, 0 ])).toEqual([ 1, 2, 3, 0 ])
  expect(uniq([ 1, 1, 2, 1 ])).toEqual([ 1, 2 ])
  expect([ 1, '1' ]).toEqual([ 1, '1' ])
  expect(uniq([ [ 42 ], [ 42 ] ])).toEqual([ [ 42 ] ])
})

Typescript test

import {uniq} from 'rambda'

describe('uniq', () => {
  it('happy', () => {
    const result = uniq([1, 2, 3, 3, 3, 1, 2, 0])
    result // $ExpectType number[]
  })
})

2 failed Ramda.uniq specs

💥 Reason for the failure: ramda pass to uniq method | ramda method uses reference equality for functions

var R = require('../../../../dist/rambda.js');
var eq = require('./shared/eq');

describe('uniq', function() {
  it('has R.equals semantics', function() {
    function Just(x) { this.value = x; }
    Just.prototype.equals = function(x) {
      return x instanceof Just && R.equals(x.value, this.value);
    };
    eq(R.uniq([-0, -0]).length, 1);
    eq(R.uniq([0, -0]).length, 2);
    eq(R.uniq([NaN, NaN]).length, 1);
    eq(R.uniq([[1], [1]]).length, 1);
    eq(R.uniq([new Just([42]), new Just([42])]).length, 1);
  it('handles null and undefined elements', function() {
    eq(R.uniq([void 0, null, void 0, null]), [void 0, null]);
  it('uses reference equality for functions', function() {
    eq(R.uniq([R.add, R.identity, R.add, R.identity, R.add, R.identity]).length, 2);
});

uniqWith

uniqWith<T, U>(uniqFn: (x: T, y: T) => boolean, list: ReadonlyArray<T>): T[]

It returns a new array containing only one copy of each element in list according to boolean returning function uniqFn.

const list = [
  {id: 0, title:'foo'},
  {id: 1, title:'bar'},
  {id: 2, title:'baz'},
  {id: 3, title:'foo'},
  {id: 4, title:'bar'},
]

const expected = [
  {id: 0, title:'foo'},
  {id: 1, title:'bar'},
  {id: 2, title:'baz'},
]

const uniqFn = (x,y) => x.title === y.title

const result = R.uniqWith(uniqFn, list)
// => `result` is equal to `expected`

Try the above R.uniqWith example in Rambda REPL

All Typescript definitions

uniqWith<T, U>(uniqFn: (x: T, y: T) => boolean, list: ReadonlyArray<T>): T[];
uniqWith<T, U>(uniqFn: (x: T, y: T) => boolean): (list: ReadonlyArray<T>) => T[];

R.uniqWith source

import { any } from './any'

export function uniqWith(fn, list){
  if (arguments.length === 1) return _list => uniqWith(fn, _list)

  let index = -1
  const len = list.length
  const willReturn = []

  while (++index < len){
    const value = list[ index ]
    const flag = any(willReturnInstance => fn(value, willReturnInstance),
      willReturn)

    if (!flag){
      willReturn.push(value)
    }
  }

  return willReturn
}

Tests

import { uniqWith } from './uniqWith'

test('happy', () => {
  const input = [
    {
      id    : 0,
      title : 'foo',
    },
    {
      id    : 1,
      title : 'bar',
    },
    {
      id    : 2,
      title : 'baz',
    },
    {
      id    : 3,
      title : 'foo',
    },
    {
      id    : 4,
      title : 'bar',
    },
  ]

  const expectedResult = [
    {
      id    : 0,
      title : 'foo',
    },
    {
      id    : 1,
      title : 'bar',
    },
    {
      id    : 2,
      title : 'baz',
    },
  ]

  const fn = (x, y) => x.title === y.title

  const result = uniqWith(fn, input)
  const curriedResult = uniqWith(fn)(input)

  expect(result).toEqual(expectedResult)

  expect(curriedResult).toEqual(expectedResult)
})

test('uniqWith', () => {
  const input = [
    {
      id    : 0,
      title : 'foo',
    },
    {
      id    : 1,
      title : 'bar',
    },
    {
      id    : 2,
      title : 'baz',
    },
    {
      id    : 3,
      title : 'foo',
    },
    {
      id    : 4,
      title : 'bar',
    },
  ]

  const expectedResult = [
    {
      id    : 0,
      title : 'foo',
    },
    {
      id    : 1,
      title : 'bar',
    },
    {
      id    : 2,
      title : 'baz',
    },
  ]

  const fn = (x, y) => x.title === y.title

  const result = uniqWith(fn, input)
  //const result = uniqWith(Ramda.eqBy(Ramda.prop('title')), input)

  expect(result).toEqual(expectedResult)
})

Typescript test

import {uniqWith} from 'rambda'

describe('uniqWith', () => {
  it('happy', () => {
    const input = [
      {
        id: 0,
        title: 'foo',
      },
      {
        id: 1,
        title: 'bar',
      },
      {
        id: 2,
        title: 'baz',
      },
      {
        id: 3,
        title: 'foo',
      },
      {
        id: 4,
        title: 'bar',
      },
    ]

    const fn = (x: any, y: any) => x.title === y.title

    const result = uniqWith(fn, input)
    result // $ExpectType { id: number; title: string; }[]
  })
})

unless

unless<T, U>(predicate: (a: T) => boolean, whenFalseFn: (a: T) => U, obj: T): U

The method returns function that will be called with argument input.

If predicate(input) returns false, then the end result will be the outcome of whenFalse(input).

In the other case, the final output will be the input itself.

const fn = R.unless(
  x => x > 2,
  x => x + 10
)

const result = [
  fn(1),
  fn(5)
]
// => [11, 5]

Try the above R.unless example in Rambda REPL

All Typescript definitions

unless<T, U>(predicate: (a: T) => boolean, whenFalseFn: (a: T) => U, obj: T): U;
unless<T, U>(predicate: (a: T) => boolean, whenFalseFn: (a: T) => U): (obj: T) => U;

R.unless source

export function unless(condition, whenFalse){
  if (arguments.length === 1){
    return whenFalseHolder => unless(condition, whenFalseHolder)
  }

  return input => {
    if (condition(input)) return input

    return whenFalse(input)
  }
}

Tests

import { inc } from './inc'
import { isNil } from './isNil'
import { unless } from './unless'

const safeInc = unless(isNil, inc)

test('happy', () => {
  expect(safeInc(null)).toBeNull()
  expect(safeInc(1)).toBe(2)
})

test('curried', () => {
  const safeIncCurried = unless(isNil)(inc)
  expect(safeInc(null)).toBeNull()
  expect(safeInc(1)).toBe(2)
})

update

update<T>(index: number, newValue: T, list: ReadonlyArray<T>): T[]

It returns a copy of list with updated element at index with newValue.

const index = 2
const newValue = 88
const list = [1, 2, 3, 4, 5]

const result = R.update(index, newValue, list)
// => [1, 2, 88, 4, 5]

Try the above R.update example in Rambda REPL

All Typescript definitions

update<T>(index: number, newValue: T, list: ReadonlyArray<T>): T[];
update<T>(index: number, newValue: T): (list: ReadonlyArray<T>) => T[];

R.update source

import { curry } from './curry'

function updateFn(
  index, newValue, list
){
  const arrClone = list.slice()

  return arrClone.fill(
    newValue, index, index + 1
  )
}

export const update = curry(updateFn)

Tests

import { update } from './update'

const list = [ 1, 2, 3 ]

test('happy', () => {
  const newValue = 8
  const index = 1
  const result = update(
    index, newValue, list
  )
  const curriedResult = update(index, newValue)(list)
  const tripleCurriedResult = update(index)(newValue)(list)

  const expected = [ 1, 8, 3 ]
  expect(result).toEqual(expected)
  expect(curriedResult).toEqual(expected)
  expect(tripleCurriedResult).toEqual(expected)
})

test('list has no such index', () => {
  const newValue = 8
  const index = 10
  const result = update(
    index, newValue, list
  )

  expect(result).toEqual(list)
})

Typescript test

import {update} from 'rambda'

describe('update', () => {
  it('happy', () => {
    const result = update(1, 0, [1, 2, 3])
    result // $ExpectType number[]
  })
})

1 failed Ramda.update specs

💥 Reason for the failure: ramda accepts an array-like object

var R = require('../../../../dist/rambda.js');
var eq = require('./shared/eq');

describe('update', function() {
  it('accepts an array-like object', function() {
    function args() {
      return arguments;
    }
    eq(R.update(2, 4, args(0, 1, 2, 3)), [0, 1, 4, 3]);
  });
});

values

values<T extends object, K extends keyof T>(obj: T): T[K][]

With correct input, this is nothing more than Object.values(obj). If obj is not an object, then it returns an empty array.

const obj = {a:1, b:2}

R.values(obj)
// => [1, 2]

Try the above R.values example in Rambda REPL

All Typescript definitions

values<T extends object, K extends keyof T>(obj: T): T[K][];

R.values source

import { type } from './type'

export function values(obj){
  if (type(obj) !== 'Object') return []

  return Object.values(obj)
}

Tests

import { values } from './values'

test('happy', () => {
  expect(values({
    a : 1,
    b : 2,
    c : 3,
  })).toEqual([ 1, 2, 3 ])
})

test('with bad input', () => {
  expect(values(null)).toEqual([])
  expect(values(undefined)).toEqual([])
  expect(values(55)).toEqual([])
  expect(values('foo')).toEqual([])
  expect(values(true)).toEqual([])
  expect(values(false)).toEqual([])
  expect(values(NaN)).toEqual([])
  expect(values(Infinity)).toEqual([])
  expect(values([])).toEqual([])
})

Typescript test

import {values} from 'rambda'

describe('values', () => {
  it('happy', () => {
    const result = values({
      a: 1,
      b: 2,
      c: 3,
    })
    result // $ExpectType number[]
  })
})

view

view<T, U>(lens: Lens): (target: T) => U

It returns the value of lens focus over target object.

const lens = R.lensProp('x')

R.view(lens, {x: 1, y: 2}) //=> 1
R.view(lens, {x: 4, y: 2}) //=> 4

Try the above R.view example in Rambda REPL

All Typescript definitions

view<T, U>(lens: Lens): (target: T) => U;
view<T, U>(lens: Lens, target: T): U;

R.view source

const Const = x => ({
  x,
  map : fn => Const(x),
})

export function view(lens, target){
  if (arguments.length === 1) return _target => view(lens, _target)

  return lens(Const)(target).x
}

wait

wait<T>(fn: Async<T>): Promise<[T, Error]>

It provides Golang-like interface for handling promises.

const [result, err] = await R.wait(R.delay(1000))
// => err is undefined
// => result is `RAMBDAX_DELAY`

Try the above R.wait example in Rambda REPL

All Typescript definitions

wait<T>(fn: Async<T>): Promise<[T, Error]>;

R.wait source

export function wait(fn){
  return new Promise(resolve => {
    fn.then(result => resolve([ result, undefined ])).catch(e =>
      resolve([ undefined, e ]))
  })
}

Tests

import { wait } from './wait'

test('happy path', async () => {
  const fn = x => Promise.resolve(x + 1)
  const [ result, err ] = await wait(fn(1))

  expect(result).toBe(2)
  expect(err).toBeUndefined()
})

test('when promise is rejected', async () => {
  const fn = x => Promise.reject(Error('foo'))
  const [ result, err ] = await wait(fn(1))

  expect(result).toBeUndefined()
  expect(err).toEqual(Error('foo'))
})

waitFor

waitFor(
  waitForTrueCondition: () => any | Promise<any>,
  howLong: number,
  loops?: number
): (input?: any) => Promise<any>

It returns true, if condition returns true within howLong milisececonds time period.

The method accepts an optional third argument loops(default to 10), which is the number of times waitForTrueCondition will be evaluated for howLong period. Once this function returns a value different from false, this value will be the final result.

Otherwise, R.waitFor will return false.

All Typescript definitions

waitFor(
  waitForTrueCondition: () => any | Promise<any>,
  howLong: number,
  loops?: number
): (input?: any) => Promise<any>;

R.waitFor source

import { delay } from './delay'
import { range } from './range'
import { type } from './type'

export function w

License

8bu/rambdax

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