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Lightweight, robust, and elegant virtual syntax highlighting using Prism.

Contents

What is this?

This package wraps Prism to output objects (ASTs) instead of a string of HTML.

Prism, through refractor, supports 290+ programming languages. Supporting all of them requires a lot of code. That’s why there are three entry points for refractor:

  • refractor/all — 297 languages
  • refractor/core — 0 languages
  • refractor (default) — 36 common languages

Bundled, minified, and gzipped, those are roughly 12.7 kB (core), 40 kB (default), and 211 kB (all).

When should I use this?

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 refractor 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).

A different package, lowlight, does the same as refractor but uses highlight.js instead. If you’re looking for a really good but rather heavy highlighter, try starry-night.

Playground

You can play with refractor on the interactive demo (Replit).

Install

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

npm install refractor

In Deno with esm.sh:

import {refractor} from 'https://esm.sh/refractor@5'

In browsers with esm.sh:

<script type="module">
  import {refractor} from 'https://esm.sh/refractor@5?bundle'
</script>

Use

import {refractor} from 'refractor'

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

console.log(tree)

Yields:

{
  type: 'root',
  children: [
    {
      type: 'element',
      tagName: 'span',
      properties: {className: ['token', 'string']},
      children: [{type: 'text', value: '"use strict"'}]
    },
    {
      type: 'element',
      tagName: 'span',
      properties: {className: ['token', 'punctuation']},
      children: [{type: 'text', value: ';'}]
    }
  ]
}

API

refractor has several entries in its export map:

  • refractor, which exports refractor and registers common grammars
  • refractor/all, which exports refractor and registers all grammars
  • refractor/core, which exports refractor and registers no grammars
  • refractor/*, where * is a language name such as markdown, which exports a syntax function as the default export

refractor

refractor.highlight(value, language)

Highlight value (code) as language (programming language).

Parameters
  • value (string) — code to highlight
  • language (string or Grammar) — programming language name, alias, or grammar
Returns

Node representing highlighted code (Root).

Example
import css from 'refractor/css'
import {refractor} from 'refractor/core'

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

Yields:

{
  type: 'root',
  children: [
    {type: 'element', tagName: 'span', properties: [Object], children: [Array]},
    {type: 'text', value: ' '},
    // …
    {type: 'text', value: ' red '},
    {type: 'element', tagName: 'span', properties: [Object], children: [Array]}
  ]
}

refractor.register(syntax)

Register a syntax.

Parameters
  • syntax (Function) — language function custom made for refractor, as in, the files in refractor/*
Example
import markdown from 'refractor/markdown'
import {refractor} from 'refractor/core'

refractor.register(markdown)

console.log(refractor.highlight('*Emphasis*', 'markdown'))

Yields:

{
  type: 'root',
  children: [
    {type: 'element', tagName: 'span', properties: [Object], children: [Array]}
  ]
}

refractor.alias(name[, alias])

Register aliases for already registered languages.

Signatures
  • alias(name, alias | list)
  • alias(aliases)
Parameters
  • language (string) — programming language name
  • alias (string) — new aliases for the programming language
  • list (Array<string>) — list of aliases
  • aliases (Record<language, alias | list>) — map of languages to aliases or lists
Example
import markdown from 'refractor/markdown'
import {refractor} from 'refractor/core'

refractor.register(markdown)

// refractor.highlight('*Emphasis*', 'mdown')
// ^ would throw: Error: Unknown language: `mdown` is not registered

refractor.alias({markdown: ['mdown', 'mkdn', 'mdwn', 'ron']})
refractor.highlight('*Emphasis*', 'mdown')
// ^ Works!

refractor.registered(aliasOrlanguage)

Check whether an alias or language is registered.

Parameters
  • aliasOrlanguage (string) — programming language name or alias
Example
import markdown from 'refractor/markdown'
import {refractor} from 'refractor/core'

console.log(refractor.registered('markdown')) //=> false

refractor.register(markdown)

console.log(refractor.registered('markdown')) //=> true

refractor.listLanguages()

List all registered languages (names and aliases).

Returns

Array<string>.

Example
import markdown from 'refractor/markdown'
import {refractor} from 'refractor/core'

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

refractor.register(markdown)

console.log(refractor.listLanguages())

Yields:

[
  'markup', // Note that `markup` (a lot of xml based languages) is a dep of markdown.
  'html',
  // …
  'markdown',
  'md'
]

Syntax

Refractor syntax function (TypeScript type).

Type
export type Syntax = ((prism: Refractor) => undefined | void) & {
  aliases?: Array<string> | undefined
  displayName: string
}

Examples

Example: serializing hast as html

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

import {toHtml} from 'hast-util-to-html'
import {refractor} from 'refractor'

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

console.log(toHtml(tree))

Yields:

<span class="token string">"use strict"</span><span class="token punctuation">;</span>

Example: turning hast into react nodes

hast trees as returned by refractor can be turned into React (or Preact) with hast-util-to-jsx-runtime:

import {toJsxRuntime} from 'hast-util-to-jsx-runtime'
import {Fragment, jsxs, jsx} from 'react/jsx-runtime'
import {refractor} from 'refractor'

const tree = refractor.highlight('"use strict";', 'js')
const reactNode = toJsxRuntime(tree, {Fragment, jsxs, jsx})

console.log(react)

Yields:

{
  '$$typeof': Symbol(react.element),
  type: 'div',
  key: 'h-1',
  ref: null,
  props: { children: [ [Object], [Object] ] },
  _owner: null,
  _store: {}
}

Data

If you’re using refractor/core, no syntaxes are included. Checked syntaxes are included if you import refractor. Unchecked syntaxes are available through refractor/all. You can import refractor/core or refractor and manually add more languages as you please.

Prism operates as a singleton: once you register a language in one place, it’ll be available everywhere.

Only these custom built syntaxes will work with refractor because Prism’s own syntaxes are made to work with global variables and are not importable.

CSS

refractor does not inject CSS for the syntax highlighted code. It does not make sense: refractor 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 Prism theme. For example, to get Prism Dark from esm.sh:

<link rel="stylesheet" href="https://esm.sh/prismjs@1.30.0/themes/prism-dark.css">

Compatibility

This package is at least compatible with all maintained versions of Node.js. As of now, that is Node.js 16+. It also works in Deno and modern browsers.

Only the custom built syntaxes in refractor/* will work with refractor as Prism’s own syntaxes are made to work with global variables and are not importable.

refractor also does not support Prism plugins, due to the same limitations, and that they almost exclusively deal with the DOM.

Security

This package is safe.

Related

Projects

Contribute

Yes please! See How to Contribute to Open Source.

License

MIT © Titus Wormer

About

Lightweight, robust, elegant virtual syntax highlighting using Prism

Topics

react syntax-highlighting html syntax virtual-dom virtual highlight vdom hast

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5.0.0 Latest
Mar 11, 2025
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