Mutative - A JavaScript library for efficient immutable updates, 10x faster than Immer by default, even faster than naive handcrafted reducer.

Writing immutable updates by hand is usually difficult, prone to errors, and cumbersome. Immer helps us write simpler immutable updates with "mutative" logic.

But its performance issue causes a runtime performance overhead. Immer must have auto-freeze enabled by default(Performance will be worse if auto-freeze is disabled), such immutable state with Immer is not common. In scenarios such as cross-processing, remote data transfer, etc., we have to constantly freeze these immutable data.

There are more parts that could be improved, such as better type inference, non-intrusive markup, support for more types of immutability, Safer immutability, and so on.

This is why Mutative was created.

Measure(ops/sec) to update 50K arrays and 1K objects, bigger is better(view source). [Mutative v0.4.0 vs Immer v9.0.19]

Naive handcrafted reducer - No Freeze x 3,713 ops/sec ±0.86% (89 runs sampled)
Mutative - No Freeze x 5,323 ops/sec ±1.69% (93 runs sampled)
Immer - No Freeze x 8 ops/sec ±0.88% (23 runs sampled)

Mutative - Freeze x 875 ops/sec ±1.20% (95 runs sampled)
Immer - Freeze x 320 ops/sec ±0.45% (92 runs sampled)

Mutative - Patches and No Freeze x 752 ops/sec ±0.16% (96 runs sampled)
Immer - Patches and No Freeze x 7 ops/sec ±1.32% (23 runs sampled)

Mutative - Patches and Freeze x 425 ops/sec ±0.33% (95 runs sampled)
Immer - Patches and Freeze x 239 ops/sec ±0.99% (89 runs sampled)

The fastest method is Mutative - No Freeze

Run yarn benchmark to reproduce them locally.

OS: macOS 12.6, CPU: Apple M1 Max, Node.js: 16.14.2

Immer relies on auto-freeze to be enabled, if auto-freeze is disabled, Immer will have a huge performance drop and Mutative will have a huge performance lead, especially with large data structures it will have a performance lead of more than 50x.

So if you are using Immer, you will have to enable auto-freeze for performance. Mutative is disabled auto-freeze by default. With the default configuration of both, we can see the performance gap between Mutative (5,323 ops/sec) and Immer (320 ops/sec).

Overall, Mutative has a huge performance lead over Immer in more performance testing scenarios. Run yarn performance to get all the performance results locally.

• Mutation makes immutable updates
• Support apply patches
• Optional freezing state
• Custom shallow copy
• Immutable and mutable data markable
• Safer mutable data access in strict mode
• Support for JSON Patch spec
• Support for reducer

Mutative has fewer bugs such as accidental draft escapes than Immer, view details.

Mutative size is 4.33KB with minified and gzipped. Immer size with same features is 4.67 KB.

Yarn

yarn add mutative

NPM

npm install mutative

CDN

• Unpkg: <script src="https://unpkg.com/mutative"></script>
• JSDelivr: <script src="https://cdn.jsdelivr.net/npm/mutative"></script>

import { create } from 'mutative';

const baseState = {
  foo: 'bar',
  list: [{ text: 'coding' }],
};

const state = create(baseState, (draft) => {
  draft.foo = 'foobar';
  draft.list.push({ text: 'learning' });
});

create(baseState, (draft) => void, options?: Options): newState

The first argument of create() is the base state. Mutative drafts it and passes it to the arguments of the draft function, and performs the draft mutation until the draft function finishes, then Mutative will finalize it and produce the new state.

Use create() for more advanced features by setting options.

Use create() for draft mutation to get a new state, which also supports currying.

import { create } from 'mutative';

const baseState = {
  foo: 'bar',
  list: [{ text: 'todo' }],
};

const state = create(baseState, (draft) => {
  draft.foo = 'foobar';
  draft.list.push({ text: 'learning' });
});

In this basic example, the changes to the draft are 'mutative' within the draft callback, and create() is finally executed with a new immutable state.

• strict - boolean, the default is false.

  Forbid accessing non-draftable values in strict mode(unless using unsafe()).

  It is recommended to enable strict in development mode and disable strict in production mode. This will ensure safe returns and also keep good performance in the production build. If the return value is mixed drafts or undefined, then use safeReturn().

• enablePatches - boolean | { pathAsArray?: boolean; arrayLengthAssignment?: boolean; }, the default is false.

  Enable patch, and return the patches/inversePatches.

  If you need to set the shape of the generated patch in more detail, then you can set pathAsArray and arrayLengthAssignment。pathAsArray default value is true, if it's true, the path will be an array, otherwise it is a string; arrayLengthAssignment default value is true, if it's true, the array length will be included in the patches, otherwise no include array length(NOTE: If arrayLengthAssignment is false, it is fully compatible with JSON Patch spec, but it may have additional performance loss).

• enableAutoFreeze - boolean, the default is false.

  Enable autoFreeze, and return frozen state, and enable circular reference checking only in development mode.

• mark - (target) => ('mutable'|'immutable'|function)

  Set a mark to determine if the value is mutable or if an instance is an immutable, and it can also return a shallow copy function(AutoFreeze and Patches should both be disabled).

• create draft

const [draft, finalize] = create(baseState);
draft.foobar.bar = 'baz';
const state = finalize();

• create producer

const producer = create((draft) => {
  draft.foobar.bar = 'baz';
});
const state = producer(baseState);

They also all support set options such as const [draft, finalize] = create(baseState, { enableAutoFreeze: true });

Use apply() for applying patches to get the new state.

import { create, apply } from 'mutative';

const baseState = {
  foo: 'bar',
  list: [{ text: 'todo' }],
};

const [state, patches, inversePatches] = create(
  baseState,
  (draft) => {
    draft.foo = 'foobar';
    draft.list.push({ text: 'learning' });
  },
  {
    enablePatches: true,
  }
);

const nextState = apply(baseState, patches);
expect(nextState).toEqual(state);
const prevState = apply(state, inversePatches);
expect(prevState).toEqual(baseState);

Get the current value from a draft.

const baseState = {
  foo: 'bar',
  list: [{ text: 'todo' }],
};

const state = create(baseState, (draft) => {
  draft.foo = 'foobar';
  draft.list.push({ text: 'learning' });
  expect(current(draft.list)).toEqual([{ text: 'todo' }, { text: 'learning' }]);
});

Get the original value from a draft.

const baseState = {
  foo: 'bar',
  list: [{ text: 'todo' }],
};

const state = create(baseState, (draft) => {
  draft.foo = 'foobar';
  draft.list.push({ text: 'learning' });
  expect(original(draft.list)).toEqual([{ text: 'todo' }]);
});

When strict mode is enabled, mutable data can only be accessed using unsafe().

const baseState = {
  list: [],
  date: new Date(),
};

const state = create(
  baseState,
  (draft) => {
    unsafe(() => {
      draft.date.setFullYear(2000);
    });
    // or return the mutable data:
    // const date = unsafe(() => draft.date);
  },
  {
    strict: true,
  }
);

Check if a value is a draft.

const baseState = {
  date: new Date(),
  list: [{ text: 'todo' }],
};

const state = create(baseState, (draft) => {
  expect(isDraft(draft.date)).toBeFalsy();
  expect(isDraft(draft.list)).toBeTruthy();
});

Check if a value is draftable

const baseState = {
  date: new Date(),
  list: [{ text: 'todo' }],
};

expect(isDraftable(baseState.date)).toBeFalsy();
expect(isDraftable(baseState.list)).toBeTruthy();

You can set a mark to determine if the value is draftable, and the mark function should be the same as passing in create() mark option.

It is used as a safe return value to ensure that this value replaces the finalized draft value or use it to return undefined explicitly.

const baseState = { id: 'test' };
const state = create(baseState as { id: string } | undefined, (draft) => {
  return safeReturn(undefined);
});
expect(state).toBe(undefined);

You don't need to use safeReturn() when the return value doesn't have any draft.

View more API docs.

• castDraft()
• castImmutable()
• Mutable<T>
• Immutable<T>
• Patches
• Patch
• Options<O, F>

• use-mutative

• Why doesn't Mutative support IE?

Mutative is a library that relies heavily on the use of the Proxy object, which is a feature of modern web browsers that allows the interception of various operations on objects. As such, Mutative may not be fully compatible with older browsers that do not support the Proxy object, such as Internet Explorer. However, these older browsers make up a very small percentage of the overall browser market, so the impact on compatibility is likely minimal.

• Why does Mutative have such good performance?

Mutative optimization focus on shallow copy optimization, more complete lazy drafts, finalization process optimization, and more.

• I'm already using Immer, can I migrate smoothly to Mutative?

Yes. Unless you have to be compatible with Internet Explorer, Mutative supports almost all of Immer features, and you can easily migrate from Immer to Mutative.

Migration is also not possible for React Native that does not support Proxy. React Native uses a new JS engine during refactoring - Hermes, and it (if < v0.59 or when using the Hermes engine on React Native < v0.64) does not support Proxy on Android, but React Native v0.64 with the Hermes engine support Proxy.

• Can Mutative be integrated with Redux?

Yes. Mutative supports return values for reducer, and redux-toolkit is considering support for configurable produce().

1. produce() -> create()

Mutative auto freezing option is disabled by default, Immer auto freezing option is enabled by default (if disabled, Immer performance will have a more huge drop).

You need to check if auto freezing has any impact on your project. If it depends on auto freezing, you can enable it yourself in Mutative.

import produce from 'immer';

const nextState = produce(baseState, (draft) => {
  draft[1].done = true;
  draft.push({ title: 'something' });
});

Use Mutative

import { create } from 'mutative';

const nextState = create(baseState, (draft) => {
  draft[1].done = true;
  draft.push({ title: 'something' });
});

2. Patches

import { produceWithPatches, applyPatches } from 'immer';

enablePatches();

const baseState = {
  age: 33,
};

const [nextState, patches, inversePatches] = produceWithPatches(
  baseState,
  (draft) => {
    draft.age++;
  }
);

const state = applyPatches(nextState, inversePatches);

expect(state).toEqual(baseState);

Use Mutative

import { create, apply } from 'mutative';

const baseState = {
  age: 33,
};

const [nextState, patches, inversePatches] = create(
  baseState,
  (draft) => {
    draft.age++;
  },
  {
    enablePatches: true,
  }
);

const state = apply(nextState, inversePatches);

expect(state).toEqual(baseState);

3. Return undefined

import produce, { nothing } from 'immer';

const nextState = produce(baseState, (draft) => {
  return nothing;
});

Use Mutative

import { create, safeReturn } from 'mutative';

const nextState = create(baseState, (draft) => {
  return safeReturn(undefined);
});

Mutative goal is to provide efficient and immutable updates. The focus is on performance improvements and providing better APIs for better development experiences. We are still working on it and welcome PRs that may help Mutative.

Development Workflow:

• Clone Mutative repo.
• Run yarn install to install all the dependencies.
• Run yarn prettier to format the code.
• yarn test --watch runs an interactive test watcher.
• Run yarn commit to make a git commit.

Mutative is MIT licensed.