Rehype Pretty Code

Rehype Pretty Code is a Rehype plugin powered by the Shiki syntax highlighter that provides beautiful code blocks for Markdown or MDX. It's fast since it avoids runtime syntax highlighting by executing at build-time, and works with new features like React Server Components.

Perfect syntax highlighting

Leverage the accuracy of VS Code's syntax highlighting engine and the popularity of its themes ecosystem — use any VS Code theme you want!

import Document, { Html, Head, Main, NextScript } from 'next/document';
 
// 🔥 Super granular and accurate highlighting
export default class MyDocument extends Document {
  static async getInitialProps(ctx) {
    const initialProps = await Document.getInitialProps(ctx);
    return { ...initialProps };
  }
 
  render() {
    return (
      <Html>
        <Head />
        <body className="bg-zinc-800 text-zinc-200">
          <Main />
          <NextScript />
        </body>
      </Html>
    );
  }
}

The theme is Moonlight II with a custom background color.

Line numbers and line highlighting are supported

import { useFloating } from '@floating-ui/react';
 
function MyComponent() {
  const { refs, floatingStyles } = useFloating();
 
  return (
    <>
      <div ref={refs.setReference} />
      <div ref={refs.setFloating} style={floatingStyles} />
    </>
  );
}

Word highlighting

import { useFloating } from '@floating-ui/react';
 
function MyComponent() {
  const { refs, floatingStyles } = useFloating();
 
  return (
    <>
      <div ref={refs.setReference} />
      <div ref={refs.setFloating} style={floatingStyles} />
    </>
  );
}

Inline code highlighting

The result of [1, 2, 3].join('-') is '1-2-3'.

Context-aware inline code

For instance, if you had the following code block:

function getStringLength(str) {
  return str.length;
}

When we refer to getStringLength as a plain variable, we can color it as a function. Same with function, or str vs. str, etc. This allows you to semantically tie inline code with the nearest code block it's referring to.

ANSI highlighting

  vite v2.8.6 dev server running at:
 
  > Local: http://localhost:3000/
  > Network: use `--host` to expose
 
  ready in 125ms.
 
8:38:02 PM [vite] hmr update /src/App.jsx

Inline ANSI: > Local: http://localhost:3000/

Installation

Install via your terminal:

npm install rehype-pretty-code shiki

Note: versions above 0.10.0 are ESM-only. If you need CommonJS support you should use v0.10.0. You can use the latest version (ESM) in Next.js, just make sure your next config file is ESM: next.config.mjs. Here's a full example: rehype-pretty-code/website/next.config.mjs

Usage

import { unified } from 'unified';
import remarkParse from 'remark-parse';
import remarkGfm from 'remark-gfm';
import remarkRehype from 'remark-rehype';
import rehypeStringify from 'rehype-stringify';
import rehypePrettyCode from 'rehype-pretty-code';
 
async function main() {
  const file = await unified()
    .use(remarkParse)
    .use(remarkGfm)
    .use(remarkRehype)
    .use(rehypePrettyCode, {
      // See Options section below.
    })
    .use(rehypeStringify)
    .process('`const numbers = [1, 2, 3]{:js}`');
 
  console.log(String(file));
}
 
main();

MDX

The following example shows how to use this package with Next.js.

// next.config.mjs
import fs from 'node:fs';
import nextMDX from '@next/mdx';
import rehypePrettyCode from 'rehype-pretty-code';
 
/** @type {import('rehype-pretty-code').Options} */
const options = {
  // See Options section below.
};
 
const withMDX = nextMDX({
  extension: /\.mdx?$/,
  options: {
    remarkPlugins: [],
    rehypePlugins: [[rehypePrettyCode, options]],
  },
});
 
/** @type {import('next').NextConfig} */
const nextConfig = { reactStrictMode: true };
 
export default withMDX(nextConfig);

Make sure you have disabled the mdxRs option for Next.js 13 / app dir, as it currently does not support Rehype plugins.

Options

To customize the theme and highlighting, options can be specified.

Code block styles

Code blocks are fully unstyled to give you full control. The features are implemented as logical indicators in the form of attributes that allows you to apply CSS yourself.

A grid style is present by default which allows line highlighting to span the entire width of a horizontally-scrollable code block.

You can disable this setting if necessary:

const options = {
  grid: false,
};

Theme

The default theme is github-dark-dimmed. Shiki has a bunch of pre-packaged themes, which can be specified as a plain string:

const options = {
  theme: 'one-dark-pro',
};

You can use your own theme as well by passing the theme JSON:

// ESM
const options = {
  theme: JSON.parse(
    fs.readFileSync(
      new URL('./themes/moonlight-ii.json', import.meta.url),
      'utf-8'
    )
  ),
};

// CJS
const options = {
  theme: JSON.parse(
    fs.readFileSync(fs.realpathSync('./themes/my-theme.json'), 'utf-8')
  ),
};

Theme background

To apply a custom background instead of inheriting the background from the theme:

const options = {
  keepBackground: false,
};

Default code language

When no code language is specified, inline code or code blocks will not be themed (nor will the background), which may appear incongruous with others.

In this case, you can specify a default language:

const options = {
  defaultLang: 'plaintext',
};

Or you can also specify default languages for inline code and code blocks separately:

const options = {
  defaultLang: {
    block: 'plaintext',
    inline: 'plaintext',
  },
};

Meta strings

Code blocks are configured via the meta string on the top codeblock fence.

Highlight lines

Place a numeric range inside {}.

```js {1-3,4}
 
```

The line <span> receives a data-highlighted-line attribute to style via CSS.

Highlight chars

A series of characters, like a literal regex.

```js /carrot/
 
```

```js /carrot/ /apple/
 
```

The chars <span> receives a data-highlighted-chars attribute to style via CSS.

To highlight only the third to fifth instances of carrot, a numeric range can be placed after the last /.

```js /carrot/3-5
 
```

Highlight only the third to fifth instances of carrot and any instances of apple.

```js /carrot/3-5 /apple/
 
```

Group highlighted chars by id

Place an id after # after the chars. This allows you to color chars differently based on their id.

```js /age/#v /name/#v /setAge/#s /setName/#s /50/#i /'Taylor'/#i
const [age, setAge] = useState(50);
const [name, setName] = useState('Taylor');
```

const [age, setAge] = useState(50);
const [name, setName] = useState('Taylor');

The chars <span> receives a data-chars-id="<id>" attribute to style via CSS.

Highlight inline code

Append {:lang}‎ (e.g. {:js}‎) to the end of inline code to highlight it like a regular code block.

This is an array `[1, 2, 3]{:js}` of numbers 1 through 3.

Highlight plain text

Append {:.token}‎ to the end of the inline code to highlight it based on a token specified in your VS Code theme. Tokens start with a . to differentiate them from a language.

The name of the function is `getStringLength{:.entity.name.function}`.

You can create a map of tokens to shorten this usage throughout your docs:

const options = {
  tokensMap: {
    fn: 'entity.name.function',
  },
};

The name of the function is `getStringLength{:.fn}`.

Titles

Add a file title to your code block, with text inside double quotes (""):

```js title="..."
 
```

Captions

Add a caption underneath your code block, with text inside double quotes (""):

```js caption="..."
 
```

Line numbers

CSS counters can be used to add line numbers.

code {
  counter-reset: line;
}
 
code > [data-line]::before {
  counter-increment: line;
  content: counter(line);
 
  /* Other styling */
  display: inline-block;
  width: 1rem;
  margin-right: 2rem;
  text-align: right;
  color: gray;
}
 
code[data-line-numbers-max-digits='2'] > [data-line]::before {
  width: 2rem;
}
 
code[data-line-numbers-max-digits='3'] > [data-line]::before {
  width: 3rem;
}

If you want to conditionally show them, use showLineNumbers:

```js showLineNumbers
 
```

<code> will have attributes data-line-numbers and data-line-numbers-max-digits="n".

If you want to start line numbers at a specific number, use showLineNumbers{number}:

```js showLineNumbers{number}
 
```

Multiple themes (dark/light mode)

Because Shiki generates themes at build time, client-side theme switching support is not built in. There are two popular options for supporting something like Dark Mode with Shiki. See the Shiki docs for more info.

Pass your themes to theme, where the keys represent the color mode:

const options = {
  theme: {
    dark: 'github-dark-dimmed',
    light: 'github-light',
  },
};

The <code> and <pre> elements will have the data attribute data-theme="<key>", e.g data-theme="light".

Now, you can use CSS to display the desired theme:

@media (prefers-color-scheme: dark) {
  pre[data-theme='light'],
  code[data-theme='light'] {
    display: none;
  }
}
 
@media (prefers-color-scheme: light), (prefers-color-scheme: no-preference) {
  pre[data-theme='dark'],
  code[data-theme='dark'] {
    display: none;
  }
}

Visitor hooks

To customize the HTML output, you can use visitor callback hooks to manipulate the hAST elements directly:

const options = {
  onVisitLine(element) {
    console.log('Visited line');
  },
  onVisitHighlightedLine(element) {
    console.log('Visited highlighted line');
  },
  onVisitHighlightedChars(element) {
    console.log('Visited highlighted chars');
  },
  onVisitTitle(element) {
    console.log('Visited title');
  },
  onVisitCaption(element) {
    console.log('Visited caption');
  },
};

Custom highlighter

To completely configure the highlighter, use the getHighlighter option to provide a Shiki highlighter instance.

In order to support light and dark modes, Rehype Pretty Code provides an options object for you to extend. The theme property is preconfigured with the light or dark theme based on your theme options.

This is helpful if you'd like to configure other Shiki options, such as langs.

import { getHighlighter, BUNDLED_LANGUAGES } from 'shiki';
 
const options = {
  getHighlighter: (options) =>
    getHighlighter({
      ...options,
      langs: [
        ...BUNDLED_LANGUAGES,
        {
          id: 'groq',
          scopeName: 'source.groq',
          path: './langs/vscode-sanity/grammars/groq.json',
        },
      ],
    }),
};

Filter meta string

If your library also parses code blocks' meta strings, it may cause conflicts with rehype-pretty-code. This option allows you to filter out some part of the meta string before the library starts parsing it.

const options = {
  filterMetaString: (string) => string.replace(/filename="[^"]*"/, ''),
};

Deployment and client-side highlighting

Copy the following files to your public directory:

/node_modules/shiki/dist/onig.wasm  ->  public/dist/onig.wasm
/node_modules/shiki/languages/      ->  public/languages/
/node_modules/shiki/themes/         ->  public/themes/

Then set the CDN path:

import { setCDN } from 'shiki';
 
setCDN('/');

This will allow Shiki to load the WASM file and themes from your public directory to perform client-side highlighting. More info here.

import { unified } from 'unified';
import rehypeStringify from 'rehype-stringify';
import remarkParse from 'remark-parse';
import remarkRehype from 'remark-rehype';
import rehypePrettyCode from 'rehype-pretty-code';
 
export default async function processMarkdown(text) {
  return await unified()
    .use(remarkParse)
    .use(remarkRehype)
    .use(rehypePrettyCode)
    .use(rehypeStringify)
    .process(text);
}

License

MIT • View on GitHub