MDX Pretty Code

A Remark plugin to make the code in your MDX docs simply beautiful. Powered by Shiki.

• ✅ Perfect VS Code highlighting (use any theme)
• ✅ Line and word highlighting
• ✅ Context-adjustable inline code highlighting
• ✅ Line numbers
• ✅ No runtime or bundle size cost

Installation

npm install @atomiks/mdx-pretty-code shiki

Usage

import {createRemarkPlugin} from '@atomiks/mdx-pretty-code';
import fs from 'fs';

const prettyCode = createRemarkPlugin({
  // Options passed to shiki.getHighlighter()
  shikiOptions: {
    // Link to your VS Code theme JSON file
    theme: JSON.parse(
      fs.readFileSync(require.resolve('./themes/my-theme.json'), 'utf-8')
    ),
  },
  // These are hooks which allow you to style the node. `node` is an element
  // using JSDOM, so you can apply any CSS.
  onVisitLine(node) {
    // Style a line node.
    Object.assign(node.style, {
      margin: '0 -1.5rem',
      padding: '0 1.5rem',
    });
  },
  onVisitHighlightedLine(node) {
    // Style a highlighted line node.
    Object.assign(node.style, {
      backgroundColor: 'rgba(0,0,0,0.1)',
    });
  },
  onVisitHighlightedWord(node) {
    // Style a highlighted word node.
    Object.assign(node.style, {
      backgroundColor: 'rgba(0,0,0,0.5)',
      padding: '0.25rem',
      borderRadius: '0.25rem',
    });
  },
});

Then pass the plugin to your MDX remarkPlugins option. For example, in next.config.js using MDX v2:

module.exports = {
  experimental: {esmExternals: true},
  webpack(config, options) {
    config.module.rules.push({
      test: /\.mdx?$/,
      use: [
        options.defaultLoaders.babel,
        {
          loader: '@mdx-js/loader',
          /** @type {import('@mdx-js/loader').Options} */
          options: {
            remarkPlugins: [prettyCode],
          },
        },
      ],
    });

    return config;
  },
};

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.

1. Load multiple themes

This will render duplicate code blocks for each theme. You can then hide the other blocks with CSS.

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

shikiOptions: {
  theme: {
    dark: JSON.parse(
      fs.readFileSync(require.resolve('./themes/dark.json'), "utf-8")
    ),
    light: JSON.parse(
      fs.readFileSync(require.resolve('./themes/light.json'), "utf-8")
    ),
  },
}

The code elements and the inline code <span data-mdx-pretty-code> wrappers will have a data attribute data-theme="[key]", e.g data-theme="light". You can target the data attribute [data-theme='dark'] to apply styles for that theme.

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

@media (prefers-color-scheme: dark) {
  code[data-theme='light'] {
    display: none;
  }
}

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

2. Use the "css-variables" theme (Shiki version 0.9.9 and above)

Note that this client-side theme is less granular than most other supported VS Code themes. Also, be aware that this will generate unstyled code if you do not define these CSS variables somewhere else on your page:

<style>
  :root {
    --shiki-color-text: rgb(248, 248, 242);
    --shiki-color-background: rgb(13 13 15);
    --shiki-token-constant: rgb(102, 217, 239);
    --shiki-token-string: rgb(230, 219, 116);
    --shiki-token-comment: rgb(93,93, 95);
    --shiki-token-keyword: rgb(249, 38, 114);
    --shiki-token-parameter: rgb(230, 219, 116);
    --shiki-token-function: rgb(166, 226, 46);
    --shiki-token-string-expression: rgb(230, 219, 116);
    --shiki-token-punctuation: rgb(230, 219, 116);
    --shiki-token-link: rgb(174, 129, 255);
  }
</style>

API

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

Line highlighting

Highlight lines 1, 2 through 4, and 6.

```js {1,2-4,6}

Word highlighting

Highlight the literal word carrot. Regex is not currently supported.

```js /carrot/

Limit word highlighting to specific instances

If you want to limit which words get highlighted, this is possible. For instance:

```js /carrot/1-2,4

The numeric range must be directly after the /.

This will only highlight the first, second, and fourth instances of carrot, but not the third, or fifth+.

Inline highlighting

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

This is `inline(){:js}` code which will be colored like a regular code block.

In your MDXProvider's components prop, modify span like so:

const mdxComponents = {
  span(props) {
    if (props['data-mdx-pretty-code'] != null) {
      return (
        <code
          data-theme={props['data-theme']}
          style={{color: props['data-color']}}
        >
          {props.children.props.children}
        </code>
      );
    }

    return <span {...props} />;
  },
};

Context-specific highlighting

Shiki will color plain variables as plain text since the highlighting has no context. But if you're referring to a variable which was colored a different way by Shiki in a code block above or below the inline code, it won't be semantic.

You can instruct MDX Pretty Code to color a word by supplying a token whose color is specified in the VS Code theme.

It must start with a . to indicate it's a token, not a language.

The function name is `hello{:.entity.name.function}`.

You can create a tokensMap to shorten this throughout your docs:

createRemarkPlugin({
  // ...
  tokensMap: {
    function: 'entity.name.function',
  },
});

Now you can just do:

The function name is `hello{:.function}`.

Note: for the token feature to work, you must have supplied a JSON object to shikiOptions.theme, not a default Shiki theme string.

Line numbers

CSS counters can be used to add line numbers.

code {
  counter-reset: line;
}

code > .line::before {
  counter-increment: line;
  content: counter(line);

  /* Other styling */
  display: inline-block;
  width: 1rem;
  margin-right: 2rem;
  text-align: right;
  color: gray;
}

Language meta

The code tag has a data-language attribute, so you can add the language information to the code block.

Sanitizing

All HTML is sanitized via sanitize-html. To configure the sanitizing options, pass sanitizeOptions, which is 1:1 with its API.

License

MIT