lowlight

Virtual syntax highlighting for virtual DOMs and non-HTML things based on highlight.js.

What is this?
When should I use this?
Install
Use
API
Examples
- Example: serializing hast as html
- Example: turning hast into preact, react, etc
Types
Data
CSS
Compatibility
Security
Related
Projects
Contribute
License

What is this?

This package uses highlight.js for syntax highlighting and outputs objects (ASTs) instead of a string of HTML. It can support 190+ programming languages.

This package is useful when you want to perform syntax highlighting in a place where serialized HTML wouldn’t work or wouldn’t work well. For example, you can use lowlight when you want to show code in a CLI by rendering to ANSI sequences, when you’re using virtual DOM frameworks (such as React or Preact) so that diffing can be performant, or when you’re working with ASTs (rehype).

You can use the similar refractor if you want to use Prism grammars instead. If you’re looking for a really good (but rather heavy) alternative, use starry-night.

Install

This package is ESM only. In Node.js (version 16+), install with npm:

npm install lowlight

In Deno with esm.sh:

import {all, common, createLowlight} from 'https://esm.sh/lowlight@3'

In browsers with esm.sh:

<script type="module">
  import {all, common, createLowlight} from 'https://esm.sh/lowlight@3?bundle'
</script>

Use

import {common, createLowlight} from 'lowlight'

const lowlight = createLowlight(common)

const tree = lowlight.highlight('js', '"use strict";')

console.dir(tree, {depth: undefined})

Yields:

{
  type: 'root',
  children: [
    {
      type: 'element',
      tagName: 'span',
      properties: {className: ['hljs-meta']},
      children: [{type: 'text', value: '"use strict"'}]
    },
    {type: 'text', value: ';'}
  ],
  data: {language: 'js', relevance: 10}
}

API

This package exports the identifiers all, common, and createLowlight. There is no default export.

`all`

Map of all (±190) grammars (Record<string, LanguageFn>).

`common`

Map of common (37) grammars (Record<string, LanguageFn>).

`createLowlight([grammars])`

Create a lowlight instance.

Parameters

grammars (Record<string, LanguageFn>, optional) — grammars to add

Returns

Lowlight (Lowlight).

`lowlight.highlight(language, value[, options])`

Highlight value (code) as language (name).

Parameters

language (string) — programming language name
value (string) — code to highlight
options (Options, optional) — configuration

Returns

Tree (Root); with the following data fields: language (string), detected programming language name; relevance (number), how sure lowlight is that the given code is in the language.

Example

import {common, createLowlight} from 'lowlight'

const lowlight = createLowlight(common)

console.log(lowlight.highlight('css', 'em { color: red }'))

Yields:

{type: 'root', children: [Array], data: {language: 'css', relevance: 3}}

`lowlight.highlightAuto(value[, options])`

Highlight value (code) and guess its programming language.

Parameters

value (string) — code to highlight
options (AutoOptions, optional) — configuration

Returns

Tree (Root); with the following data fields: language (string), detected programming language name; relevance (number), how sure lowlight is that the given code is in the language.

Example

import {common, createLowlight} from 'lowlight'

const lowlight = createLowlight(common)

console.log(lowlight.highlightAuto('"hello, " + name + "!"'))

Yields:

{type: 'root', children: [Array], data: {language: 'arduino', relevance: 2}}

`lowlight.listLanguages()`

List registered languages.

Returns

Names of registered language (Array<string>).

Example

import {createLowlight} from 'lowlight'
import markdown from 'highlight.js/lib/languages/markdown'

const lowlight = createLowlight()

console.log(lowlight.listLanguages()) // => []

lowlight.register({markdown})

console.log(lowlight.listLanguages()) // => ['markdown']

`lowlight.register(grammars)`

Signatures

register(name, grammar)
register(grammars)

Parameters

name (string) — programming language name
grammar (LanguageFn) — grammar
grammars (Record<string, LanguageFn>, optional) — grammars

Returns

Nothing (undefined).

Example

import {createLowlight} from 'lowlight'
import xml from 'highlight.js/lib/languages/xml'

const lowlight = createLowlight()

lowlight.register({xml})

// Note: `html` is an alias for `xml`.
console.log(lowlight.highlight('html', '<em>Emphasis</em>'))

Yields:

{type: 'root', children: [Array], data: {language: 'html', relevance: 2}}

`lowlight.registerAlias(aliases)`

Signatures

registerAlias(aliases)
registerAlias(name, alias)

Parameters

aliases (Record<string, Array<string> | string>) — map of programming language names to one or more aliases
name (string) — programming language name
alias (Array<string> | string) — one or more aliases for the programming language

Returns

Nothing (undefined).

Example

import {createLowlight} from 'lowlight'
import markdown from 'highlight.js/lib/languages/markdown'

const lowlight = createLowlight()

lowlight.register({markdown})

// lowlight.highlight('mdown', '<em>Emphasis</em>')
// ^ would throw: Error: Unknown language: `mdown` is not registered

lowlight.registerAlias({markdown: ['mdown', 'mkdn', 'mdwn', 'ron']})
lowlight.highlight('mdown', '<em>Emphasis</em>')
// ^ Works!

`lowlight.registered(aliasOrlanguage)`

Check whether an alias or name is registered.

Parameters

aliasOrlanguage (string) — name of a language or alias for one

Returns

Whether aliasOrName is registered (boolean).

Example

import {createLowlight} from 'lowlight'
import javascript from 'highlight.js/lib/languages/javascript'

const lowlight = createLowlight({javascript})

console.log(lowlight.registered('funkyscript')) // => `false`

lowlight.registerAlias({javascript: 'funkyscript'})
console.log(lowlight.registered('funkyscript')) // => `true`

`AutoOptions`

Configuration for highlightAuto (TypeScript type).

Fields

prefix (string, default: 'hljs-') — class prefix
subset (Array<string>, default: all registered languages) — list of allowed languages

`LanguageFn`

Highlight.js grammar (TypeScript type).

Type

type {LanguageFn} from 'highlight.js'

`Options`

Configuration for highlight (TypeScript type).

Fields

prefix (string, default: 'hljs-') — class prefix

Examples

Example: serializing hast as html

hast trees as returned by lowlight can be serialized with hast-util-to-html:

import {common, createLowlight} from 'lowlight'
import {toHtml} from 'hast-util-to-html'

const lowlight = createLowlight(common)

const tree = lowlight.highlight('js', '"use strict";')

console.log(toHtml(tree))

Yields:

<span class="hljs-meta">"use strict"</span>;

Example: turning hast into preact, react, etc

hast trees as returned by lowlight can be turned into nodes of any framework that supports JSX, such as preact, react, solid, svelte, vue, and more, with hast-util-to-jsx-runtime:

import {toJsxRuntime} from 'hast-util-to-jsx-runtime'
// @ts-expect-error: react types don’t type these.
import {Fragment, jsx, jsxs} from 'react/jsx-runtime'
import {common, createLowlight} from 'lowlight'

const lowlight = createLowlight(common)

const tree = lowlight.highlight('js', '"use strict";')

console.log(toJsxRuntime(tree, {Fragment, jsx, jsxs}))

Yields:

{
  $$typeof: Symbol(react.element),
  type: Symbol(react.fragment),
  key: null,
  ref: null,
  props: {children: [[Object], ';']},
  _owner: null,
  _store: {}
}

Types

This package is fully typed with TypeScript. It exports the additional types AutoOptions, LanguageFn, and Options.

It also registers root.data with @types/hast. If you’re working with the data fields, make sure to import this package somewhere in your types, as that registers the new fields on the file.

/**
 * @typedef {import('hast').Root} Root
 *
 * @typedef {import('lowlight')}
 */

import {VFile} from 'vfile'

/** @type {Root} */
const root = {type: 'root', children: []}

console.log(root.data?.language) //=> TS now knows that this is a `string?`.

Data

If you’re using createLowlight(), no syntaxes are included yet. You can import all or common and pass them, such as with createLowlight(all). Checked syntaxes are included in common. All syntaxes are included in all.

You can also manually import syntaxes from highlight.js/lib/languages/xxx, where xxx is the name, such as 'highlight.js/lib/languages/wasm'.

[ ] 1c — 1C:Enterprise
[ ] abnf — Augmented Backus-Naur Form
[ ] accesslog — Apache Access Log
[ ] actionscript (as) — ActionScript
[ ] ada — Ada
[ ] angelscript (asc) — AngelScript
[ ] apache (apacheconf) — Apache config
[ ] applescript (osascript) — AppleScript
[ ] arcade — ArcGIS Arcade
[x] arduino (ino) — Arduino
[ ] armasm (arm) — ARM Assembly
[ ] asciidoc (adoc) — AsciiDoc
[ ] aspectj — AspectJ
[ ] autohotkey (ahk) — AutoHotkey
[ ] autoit — AutoIt
[ ] avrasm — AVR Assembly
[ ] awk — Awk
[ ] axapta (x++) — X++
[x] bash (sh) — Bash
[ ] basic — BASIC
[ ] bnf — Backus–Naur Form
[ ] brainfuck (bf) — Brainfuck
[x] c (h) — C
[ ] cal — C/AL
[ ] capnproto (capnp) — Cap’n Proto
[ ] ceylon — Ceylon
[ ] clean (icl, dcl) — Clean
[ ] clojure (clj, edn) — Clojure
[ ] clojure-repl — Clojure REPL
[ ] cmake (cmake.in) — CMake
[ ] coffeescript (coffee, cson, iced) — CoffeeScript
[ ] coq — Coq
[ ] cos (cls) — Caché Object Script
[x] cpp (cc, c++, h++, hpp, hh, hxx, cxx) — C++
[ ] crmsh (crm, pcmk) — crmsh
[ ] crystal (cr) — Crystal
[x] csharp (cs, c#) — C#
[ ] csp — CSP
[x] css — CSS
[ ] d — D
[ ] dart — Dart
[ ] delphi (dpr, dfm, pas, pascal) — Delphi
[x] diff (patch) — Diff
[ ] django (jinja) — Django
[ ] dns (bind, zone) — DNS Zone
[ ] dockerfile (docker) — Dockerfile
[ ] dos (bat, cmd) — Batch file (DOS)
[ ] dsconfig — undefined
[ ] dts — Device Tree
[ ] dust (dst) — Dust
[ ] ebnf — Extended Backus-Naur Form
[ ] elixir (ex, exs) — Elixir
[ ] elm — Elm
[ ] erb — ERB
[ ] erlang (erl) — Erlang
[ ] erlang-repl — Erlang REPL
[ ] excel (xlsx, xls) — Excel formulae
[ ] fix — FIX
[ ] flix — Flix
[ ] fortran (f90, f95) — Fortran
[ ] fsharp (fs, f#) — F#
[ ] gams (gms) — GAMS
[ ] gauss (gss) — GAUSS
[ ] gcode (nc) — G-code (ISO 6983)
[ ] gherkin (feature) — Gherkin
[ ] glsl — GLSL
[ ] gml — GML
[x] go (golang) — Go
[ ] golo — Golo
[ ] gradle — Gradle
[x] graphql (gql) — GraphQL
[ ] groovy — Groovy
[ ] haml — HAML
[ ] handlebars (hbs, html.hbs, html.handlebars, htmlbars) — Handlebars
[ ] haskell (hs) — Haskell
[ ] haxe (hx) — Haxe
[ ] hsp — HSP
[ ] http (https) — HTTP
[ ] hy (hylang) — Hy
[ ] inform7 (i7) — Inform 7
[x] ini (toml) — TOML, also INI
[ ] irpf90 — IRPF90
[ ] isbl — ISBL
[x] java (jsp) — Java
[x] javascript (js, jsx, mjs, cjs) — JavaScript
[ ] jboss-cli (wildfly-cli) — JBoss CLI
[x] json — JSON
[ ] julia — Julia
[ ] julia-repl (jldoctest) — Julia REPL
[x] kotlin (kt, kts) — Kotlin
[ ] lasso (ls, lassoscript) — Lasso
[ ] latex (tex) — LaTeX
[ ] ldif — LDIF
[ ] leaf — Leaf
[x] less — Less
[ ] lisp — Lisp
[ ] livecodeserver — LiveCode
[ ] livescript (ls) — LiveScript
[ ] llvm — LLVM IR
[ ] lsl — LSL (Linden Scripting Language)
[x] lua — Lua
[x] makefile (mk, mak, make) — Makefile
[x] markdown (md, mkdown, mkd) — Markdown
[ ] mathematica (mma, wl) — Mathematica
[ ] matlab — Matlab
[ ] maxima — Maxima
[ ] mel — MEL
[ ] mercury (m, moo) — Mercury
[ ] mipsasm (mips) — MIPS Assembly
[ ] mizar — Mizar
[ ] mojolicious — Mojolicious
[ ] monkey — Monkey
[ ] moonscript (moon) — MoonScript
[ ] n1ql — N1QL
[ ] nestedtext (nt) — Nested Text
[ ] nginx (nginxconf) — Nginx config
[ ] nim — Nim
[ ] nix (nixos) — Nix
[ ] node-repl — Node REPL
[ ] nsis — NSIS
[x] objectivec (mm, objc, obj-c, obj-c++, objective-c++) — Objective-C
[ ] ocaml (ml) — OCaml
[ ] openscad (scad) — OpenSCAD
[ ] oxygene — Oxygene
[ ] parser3 — Parser3
[x] perl (pl, pm) — Perl
[ ] pf (pf.conf) — Packet Filter config
[ ] pgsql (postgres, postgresql) — PostgreSQL
[x] php — undefined
[x] php-template — PHP template
[x] plaintext (text, txt) — Plain text
[ ] pony — Pony
[ ] powershell (pwsh, ps, ps1) — PowerShell
[ ] processing (pde) — Processing
[ ] profile — Python profiler
[ ] prolog — Prolog
[ ] properties — .properties
[ ] protobuf (proto) — Protocol Buffers
[ ] puppet (pp) — Puppet
[ ] purebasic (pb, pbi) — PureBASIC
[x] python (py, gyp, ipython) — Python
[x] python-repl (pycon) — undefined
[ ] q (k, kdb) — Q
[ ] qml (qt) — QML
[x] r — R
[ ] reasonml (re) — ReasonML
[ ] rib — RenderMan RIB
[ ] roboconf (graph, instances) — Roboconf
[ ] routeros (mikrotik) — MikroTik RouterOS script
[ ] rsl — RenderMan RSL
[x] ruby (rb, gemspec, podspec, thor, irb) — Ruby
[ ] ruleslanguage — Oracle Rules Language
[x] rust (rs) — Rust
[ ] sas — SAS
[ ] scala — Scala
[ ] scheme (scm) — Scheme
[ ] scilab (sci) — Scilab
[x] scss — SCSS
[x] shell (console, shellsession) — Shell Session
[ ] smali — Smali
[ ] smalltalk (st) — Smalltalk
[ ] sml (ml) — SML (Standard ML)
[ ] sqf — SQF
[x] sql — SQL
[ ] stan (stanfuncs) — Stan
[ ] stata (do, ado) — Stata
[ ] step21 (p21, step, stp) — STEP Part 21
[ ] stylus (styl) — Stylus
[ ] subunit — SubUnit
[x] swift — Swift
[ ] taggerscript — Tagger Script
[ ] tap — Test Anything Protocol
[ ] tcl (tk) — Tcl
[ ] thrift — Thrift
[ ] tp — TP
[ ] twig (craftcms) — Twig
[x] typescript (ts, tsx, mts, cts) — TypeScript
[ ] vala — Vala
[x] vbnet (vb) — Visual Basic .NET
[ ] vbscript (vbs) — VBScript
[ ] vbscript-html — VBScript in HTML
[ ] verilog (v, sv, svh) — Verilog
[ ] vhdl — VHDL
[ ] vim — Vim Script
[x] wasm — WebAssembly
[ ] wren — Wren
[ ] x86asm — Intel x86 Assembly
[ ] xl (tao) — XL
[x] xml (html, xhtml, rss, atom, xjb, xsd, xsl, plist, wsf, svg) — HTML, XML
[ ] xquery (xpath, xq, xqm) — XQuery
[x] yaml (yml) — YAML
[ ] zephir (zep) — Zephir

CSS

lowlight does not inject CSS for the syntax highlighted code (because well, lowlight doesn’t have to be turned into HTML and might not run in a browser!). If you are in a browser, you can use any highlight.js theme. For example, to get GitHub Dark from cdnjs:

<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/11.8.0/styles/github-dark.min.css">

Compatibility

This package is compatible with maintained versions of Node.js.

When we cut a new major release, we drop support for unmaintained versions of Node. This means we try to keep the current release line, lowlight@^3, compatible with Node.js 16.