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readme.md

rehype-katex

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rehype plugin to render elements with a language-math class with KaTeX.

Contents

What is this?

This package is a unified (rehype) plugin to render math. You can add classes to HTML elements, use fenced code in markdown, or combine with remark-math for a $C$ syntax extension.

When should I use this?

This project is useful as it renders math with KaTeX at compile time, which means that there is no client side JavaScript needed.

A different plugin, rehype-mathjax, does the same but with MathJax.

Install

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

npm install rehype-katex

In Deno with esm.sh:

import rehypeKatex from 'https://esm.sh/rehype-katex@7'

In browsers with esm.sh:

<script type="module">
  import rehypeKatex from 'https://esm.sh/rehype-katex@7?bundle'
</script>

Use

Say our document input.html contains:

<p>
  Lift(<code class="language-math">L</code>) can be determined by Lift Coefficient
  (<code class="language-math">C_L</code>) like the following equation.
</p>
<pre><code class="language-math">
  L = \frac{1}{2} \rho v^2 S C_L
</code></pre>

…and our module example.js contains:

import rehypeDocument from 'rehype-document'
import rehypeKatex from 'rehype-katex'
import rehypeParse from 'rehype-parse'
import rehypeStringify from 'rehype-stringify'
import {read, write} from 'to-vfile'
import {unified} from 'unified'

const file = await unified()
  .use(rehypeParse, {fragment: true})
  .use(rehypeDocument, {
    // Get the latest one from: <https://katex.org/docs/browser>.
    css: 'https://cdn.jsdelivr.net/npm/katex@0.16.8/dist/katex.min.css'
  })
  .use(rehypeKatex)
  .use(rehypeStringify)
  .process(await read('input.html'))

file.basename = 'output.html'
await write(file)

…then running node example.js creates an output.html with:

<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>input</title>
<meta content="width=device-width, initial-scale=1" name="viewport">
<link href="https://cdn.jsdelivr.net/npm/katex@0.16.8/dist/katex.min.css" rel="stylesheet">
</head>
<body>
<p>
  Lift(<span class="katex"><!--…--></span>) can be determined by Lift Coefficient
  (<span class="katex"><!--…--></span>) like the following equation.
</p>
<span class="katex-display"><!--…--></span>
</body>
</html>

…open output.html in a browser to see the rendered math.

API

This package exports no identifiers. The default export is rehypeKatex.

unified().use(rehypeKatex[, options])

Render elements with a language-math (or math-display, math-inline) class with KaTeX.

Parameters
  • options (Options) — configuration
Returns

Transform (Transformer).

Options

Configuration (TypeScript type).

Type
import {KatexOptions} from 'katex'

type Options = Omit<KatexOptions, 'displayMode' | 'throwOnError'>

See Options on katex.org for more info.

Markdown

This plugin supports the syntax extension enabled by remark-math. It also supports math generated by using fenced code:

```math
C_L
```

HTML

The content of any element with a language-math, math-inline, or math-display class is transformed. The elements are replaced by what KaTeX renders. Either a math-display class or using <pre><code class="language-math"> will result in “display” math: math that is a centered block on its own line.

CSS

The HTML produced by KaTeX requires CSS to render correctly. You should use katex.css somewhere on the page where the math is shown to style it properly. At the time of writing, the last version is:

<!-- Get the latest one from: https://katex.org/docs/browser -->
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/katex@0.16.8/dist/katex.min.css">

Types

This package is fully typed with TypeScript. It exports the additional type Options.

Compatibility

Projects maintained by the unified collective are 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, rehype-katex@^7, compatible with Node.js 16.

This plugin works with unified version 6+ and rehype version 4+.

Security

Assuming you trust KaTeX, using rehype-katex is safe. A vulnerability in it could open you to a cross-site scripting (XSS) attack. Be wary of user input and use rehype-sanitize.

When you don’t trust user content but do trust KaTeX, run rehype-katex after rehype-sanitize:

import rehypeKatex from 'rehype-katex'
import rehypeSanitize, {defaultSchema} from 'rehype-sanitize'
import rehypeStringify from 'rehype-stringify'
import remarkMath from 'remark-math'
import remarkParse from 'remark-parse'
import remarkRehype from 'remark-rehype'
import {unified} from 'unified'

const file = await unified()
  .use(remarkParse)
  .use(remarkMath)
  .use(remarkRehype)
  .use(rehypeSanitize, {
    ...defaultSchema,
    attributes: {
      ...defaultSchema.attributes,
      // The `language-*` regex is allowed by default.
      code: [['className', /^language-./, 'math-inline', 'math-display']]
    }
  })
  .use(rehypeKatex)
  .use(rehypeStringify)
  .process('$C$')

console.log(String(file))

Related

Contribute

See contributing.md in remarkjs/.github for ways to get started. See support.md for ways to get help.

This project has a code of conduct. By interacting with this repository, organization, or community you agree to abide by its terms.

License

MIT © Junyoung Choi