# rehype-mathjax

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**[rehype][]** plugin to render elements with a `language-math` class with
[MathJax][].

## Contents

*   [What is this?](#what-is-this)
*   [When should I use this?](#when-should-i-use-this)
*   [Install](#install)
*   [Use](#use)
*   [API](#api)
    *   [`unified().use(rehypeMathjax[, options])`](#unifieduserehypemathjax-options)
    *   [`Options`](#options)
*   [Markdown](#markdown)
*   [HTML](#html)
*   [CSS](#css)
*   [Types](#types)
*   [Compatibility](#compatibility)
*   [Security](#security)
*   [Related](#related)
*   [Contribute](#contribute)
*   [License](#license)

## 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`][remark-math] for a `$C$` syntax extension.

## When should I use this?

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

A different plugin, [`rehype-katex`][rehype-katex], does the same but with
[KaTeX][].

## Install

This package is [ESM only][esm].
In Node.js (version 18+), install with [npm][]:

```sh
npm install rehype-mathjax
```

In Deno with [`esm.sh`][esmsh]:

```js
import rehypeMathjax from 'https://esm.sh/rehype-mathjax@5'
```

In browsers with [`esm.sh`][esmsh]:

```html
<script type="module">
  import rehypeMathjax from 'https://esm.sh/rehype-mathjax@5?bundle'
</script>
```

## Use

Say our document `input.html` contains:

```html
<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:

```js
import rehypeMathjax from 'rehype-mathjax'
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(rehypeMathjax)
  .use(rehypeStringify)
  .process(await read('input.html'))

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

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

```html
<p>
  Lift(<mjx-container class="MathJax" jax="SVG"><!--…--></mjx-container>) can be determined by Lift Coefficient
  (<mjx-container class="MathJax" jax="SVG"><!--…--></mjx-container>) like the following equation.
</p>
<mjx-container class="MathJax" jax="SVG" display="true"><!--…--></mjx-container>
<style>
mjx-container[jax="SVG"] {
  direction: ltr;
}
/* … */
</style>
```

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

## API

This package has an export map with several entries for plugins using different
strategies:

*   `rehype-mathjax/browser` — browser (±1kb)
*   `rehype-mathjax/chtml` — [CHTML][mathjax-chtml] (±154kb)
*   `rehype-mathjax/svg` — [SVG][mathjax-svg] (±566kb)
*   `rehype-mathjax` — same as SVG

Each module exports the plugin [`rehypeMathjax`][api-rehype-mathjax] as
the default export.

### `unified().use(rehypeMathjax[, options])`

Render elements with a `language-math` (or `math-display`, `math-inline`)
class with [MathJax][].

###### Parameters

*   `options` ([`Options`][api-options], typically optional)
    — configuration

###### Returns

Transform ([`Transformer`][unified-transformer]).

### `Options`

Configuration (TypeScript type).

###### Fields

*   `chtml` (`unknown`, optional)
    — configuration for the output, when CHTML;
    see [*CommonHTML Output Processor Options* on
    `mathjax.org`][mathjax-chtml-options]
*   `svg` (`unknown`, optional)
    — configuration for the output, when SVG;
    see [*SVG Output Processor Options* on
    `mathjax.org`][mathjax-svg-options]
*   `tex` (`unknown`, optional)
    — configuration for the input TeX;
    see [*TeX Input Processor Options* on
    `mathjax.org`][mathjax-tex-options]

###### Notes

When using `rehype-mathjax/browser`, only `options.tex.displayMath` and
`options.tex.inlineMath` are used.
That plugin will use the first delimiter pair in those fields to wrap
math.
Then you need to load MathJax yourself on the client and start it with the
same markers.
You can pass other options on the client.

When using `rehype-mathjax/chtml`, `options.chtml.fontURL` is required.
For example:

```js
  // …
  .use(rehypeMathjaxChtml, {
    chtml: {
      fontURL: 'https://cdn.jsdelivr.net/npm/mathjax@3/es5/output/chtml/fonts/woff-v2'
    }
  })
  // …
```

## Markdown

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

````markdown
```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 MathJax 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 MathJax does not require any extra CSS to render correctly.

## Types

This package is fully typed with [TypeScript][].
It exports the additional type [`Options`][api-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-mathjax@^6`,
compatible with Node.js 18.

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

## Security

Assuming you trust MathJax, using `rehype-mathjax` is safe.
A vulnerability in it could open you to a
[cross-site scripting (XSS)][wiki-xss] attack.
Be wary of user input and use [`rehype-sanitize`][rehype-sanitize].

When you don’t trust user content but do trust MathJax, run `rehype-mathjax`
*after* `rehype-sanitize`:

```js
import rehypeMathjax from 'rehype-mathjax'
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(rehypeMathjax)
  .use(rehypeStringify)
  .process('$C$')

console.log(String(file))
```

## Related

*   [`rehype-katex`][rehype-katex]
    — same but with KaTeX
*   [`rehype-highlight`](https://github.com/rehypejs/rehype-highlight)
    — highlight code blocks
*   [`rehype-autolink-headings`](https://github.com/rehypejs/rehype-autolink-headings)
    — add links to headings
*   [`rehype-sanitize`](https://github.com/rehypejs/rehype-sanitize)
    — sanitize HTML
*   [`rehype-document`](https://github.com/rehypejs/rehype-document)
    — wrap a document around the tree

## Contribute

See [`contributing.md`][contributing] in [`remarkjs/.github`][health] for ways
to get started.
See [`support.md`][support] for ways to get help.

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

## License

[MIT][license] © [TANIGUCHI Masaya][author]

<!-- Definitions -->

[build-badge]: https://github.com/remarkjs/remark-math/workflows/main/badge.svg

[build]: https://github.com/remarkjs/remark-math/actions

[coverage-badge]: https://img.shields.io/codecov/c/github/remarkjs/remark-math.svg

[coverage]: https://codecov.io/github/remarkjs/remark-math

[downloads-badge]: https://img.shields.io/npm/dm/rehype-mathjax.svg

[downloads]: https://www.npmjs.com/package/rehype-mathjax

[size-badge]: https://img.shields.io/bundlejs/size/rehype-mathjax

[size]: https://bundlejs.com/?q=rehype-mathjax

[sponsors-badge]: https://opencollective.com/unified/sponsors/badge.svg

[backers-badge]: https://opencollective.com/unified/backers/badge.svg

[collective]: https://opencollective.com/unified

[chat-badge]: https://img.shields.io/badge/chat-discussions-success.svg

[chat]: https://github.com/remarkjs/remark/discussions

[npm]: https://docs.npmjs.com/cli/install

[esm]: https://gist.github.com/sindresorhus/a39789f98801d908bbc7ff3ecc99d99c

[esmsh]: https://esm.sh

[health]: https://github.com/remarkjs/.github

[contributing]: https://github.com/remarkjs/.github/blob/main/contributing.md

[support]: https://github.com/remarkjs/.github/blob/main/support.md

[coc]: https://github.com/remarkjs/.github/blob/main/code-of-conduct.md

[license]: https://github.com/remarkjs/remark-math/blob/main/license

[author]: https://rokt33r.github.io

[katex]: https://github.com/Khan/KaTeX

[mathjax-svg]: http://docs.mathjax.org/en/latest/output/svg.html

[mathjax-chtml]: http://docs.mathjax.org/en/latest/output/html.html

[mathjax-tex-options]: http://docs.mathjax.org/en/latest/options/input/tex.html

[mathjax-svg-options]: http://docs.mathjax.org/en/latest/options/output/svg.html

[mathjax-chtml-options]: http://docs.mathjax.org/en/latest/options/output/chtml.html

[rehype]: https://github.com/rehypejs/rehype

[rehype-sanitize]: https://github.com/rehypejs/rehype-sanitize

[typescript]: https://www.typescriptlang.org

[unified]: https://github.com/unifiedjs/unified

[unified-transformer]: https://github.com/unifiedjs/unified#transformer

[wiki-xss]: https://en.wikipedia.org/wiki/Cross-site_scripting

[mathjax]: https://mathjax.org/

[remark-math]: ../remark-math/

[rehype-katex]: ../rehype-katex/

[api-options]: #options

[api-rehype-mathjax]: #unifieduserehypemathjax-options