emphasize

ANSI syntax highlighting for your terminal.

Contents

• What is this?
• When should I use this?
• Install
• Use
• API
  • emphasize.highlight(language, value[, sheet])
  • emphasize.highlightAuto(value[, sheet | options])
  • emphasize.registerLanguage(language, syntax)
  • emphasize.registerAlias(language, alias)
  • emphasize.registered(aliasOrlanguage)
  • emphasize.listLanguages()
  • Sheet
• Types
• Compatibility
• Security
• Contribute
• License

What is this?

This package wraps highlight.js through lowlight to output ANSI syntax highlighting instead of HTML.

highlight.js, through lowlight, supports 190+ programming languages. Supporting all of them requires a lot of code. That’s why there are three entry points for emphasize:

• lib/core.js — 0 languages
• lib/common.js (default) — 37 languages
• lib/all.js — 192 languages

Bundled, minified, and gzipped, those are roughly 9.7 kB, 47 kB, and 290 kB.

When should I use this?

This package is useful when you want to display code on a terminal.

Install

This package is ESM only. In Node.js (version 14.14+, 16.0+), install with npm:

npm install emphasize

In Deno with esm.sh:

import {emphasize} from 'https://esm.sh/emphasize@6'

In browsers with esm.sh:

<script type="module">
  import {emphasize} from 'https://esm.sh/emphasize@6?bundle'
</script>

Use

Say example.css looks as follows:

@font-face {
  font-family: Alpha;
  src: url('Bravo.otf');
}

body, .charlie, #delta {
  color: #bada55;
  background-color: rgba(33, 33, 33, 0.33);
  font-family: "Alpha", sans-serif;
}

@import url(echo.css);

@media print {
  a[href^=http]::after {
    content: attr(href)
  }
}

…and example.js contains the following:

import fs from 'node:fs/promises'
import {emphasize} from 'emphasize'

const doc = String(await fs.readFile('example.css'))

const output = emphasize.highlightAuto(doc).value

console.log(output)

…now running node example.js yields:

\x1B[32m@font-face\x1B[39m {
  \x1B[33mfont-family\x1B[39m: Alpha;
  \x1B[33msrc\x1B[39m: \x1B[31murl\x1B[39m(\x1B[36m'Bravo.otf'\x1B[39m);
}

\x1B[32mbody\x1B[39m, \x1B[34m.charlie\x1B[39m, \x1B[34m#delta\x1B[39m {
  \x1B[33mcolor\x1B[39m: \x1B[36m#bada55\x1B[39m;
  \x1B[33mbackground-color\x1B[39m: \x1B[31mrgba\x1B[39m(\x1B[36m33\x1B[39m, \x1B[36m33\x1B[39m, \x1B[36m33\x1B[39m, \x1B[36m0.33\x1B[39m);
  \x1B[33mfont-family\x1B[39m: \x1B[36m"Alpha"\x1B[39m, sans-serif;
}

\x1B[32m@import\x1B[39m url(echo.css);

\x1B[32m@media\x1B[39m print {
  \x1B[32ma\x1B[39m\x1B[35m[href^=http]\x1B[39m\x1B[35m::after\x1B[39m {
    \x1B[33mcontent\x1B[39m: \x1B[31mattr\x1B[39m(href)
  }
}

…which looks as follows:

API

This package exports the identifier emphasize. There is no default export.

emphasize.highlight(language, value[, sheet])

Highlight value (code) as language (name).

Parameters

• language (string) — programming language name
• value (string) — code to highlight
• sheet (Sheet?, optional) — configure the theme

Returns

value with ANSI sequences (string).

emphasize.highlightAuto(value[, sheet | options])

Highlight value (code) and guess its programming language.

Parameters

• value (string) — code to highlight
• options.sheet (Sheet?, optional) — configure the theme
• options.subset (Array<string>, default: all registered language names) — list of allowed languages

Returns

value with ANSI sequences (string).

emphasize.registerLanguage(language, syntax)

Register a language.

Parameters

• language (string) — programming language name
• syntax (HighlightSyntax) — highlight.js syntax

Note

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

emphasize.registerAlias(language, alias)

Register aliases for already registered languages.

Signatures

• registerAlias(language, alias|list)
• registerAlias(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

emphasize.registered(aliasOrlanguage)

Check whether an alias or language is registered.

Parameters

• aliasOrlanguage (string) — name of a registered language or alias

Returns

Whether aliasOrlanguage is registered (boolean).

emphasize.listLanguages()

List registered languages.

Returns

Names of registered language (Array<string>).

Sheet

A sheet is an object mapping highlight.js classes to functions. The hljs- prefix must not be used in those classes. The “descendant selector” (a space) is supported.

Those functions receive a value (string), which they should wrap in ANSI sequences and return. For convenience, chalk’s chaining of styles is suggested.

An abbreviated example is as follows:

{
  'comment': chalk.gray,
  'meta meta-string': chalk.cyan,
  'meta keyword': chalk.magenta,
  'emphasis': chalk.italic,
  'strong': chalk.bold,
  'formula': chalk.inverse
}

Types

This package is fully typed with TypeScript. It exports the additional types Sheet and AutoOptions.

Compatibility

This package is at least compatible with all maintained versions of Node.js. As of now, that is Node.js 14.14+ and 16.0+. It also works in Deno and modern browsers.

Security

This package is safe.

Contribute

Yes please! See How to Contribute to Open Source.

License

MIT © Titus Wormer

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