rehype-prism-plus

rehype-prism-plus

rehype plugin to highlight code blocks in HTML with Prism with additional line highlighting and line numbers functionalities.

Inspired by and uses a compatible API as @mapbox/rehype-prism with additional support for line-highlighting and line numbers.

Tested to work with xdm and mdx v2 libraries such as mdx-bundler. If you are using mdx v1 libraries such as next-mdx-remote, you will need to patch it with the fixMetaPlugin discussed in https://github.com/timlrx/rehype-prism-plus/issues/20.

An appropriate stylesheet should be loaded to style the language tokens, format line numbers and highlight lines.

Best suited for usage in Node. If you would like to perform syntax highlighting in the browser, you should look into less heavy ways to use refractor.

Installation

This package is ESM only: Node 12+ is needed to use it and it must be imported instead of required.

npm install rehype-prism-plus

Usage

Use this package as a rehype plugin.

Some examples of how you might do that:

import rehype from 'rehype'
import rehypePrism from 'rehype-prism-plus'

rehype().use(rehypePrism).process(/* some html */)

Here's an example of syntax highlighting in Markdown, with xdm

import { compile } from 'xdm'
import rehypePrism from 'rehype-prism-plus'

async function main(code) {
  console.log(String(await compile(code, { rehypePlugins: [rehypePrism] })))
}

main(`~~~js
console.log(1)
~~~`)

Sample markdown to HTML output

Input:

```js {1,3-4} showLineNumbers
function fancyAlert(arg) {
  if (arg) {
    $.facebox({ div: '#foo' })
  }
}
```

HTML Output:

<code class="language-js">
  <div class="code-line line-number highlight-line" line="1">
    <span class="keyword">function</span>
    <span class="function">fancyAlert</span><span class="punctuation">(</span
    ><span class="">arg</span><span class="punctuation">)</span>
    <span class="punctuation">{</span>
  </div>
  <div class="code-line line-number highlight-line" line="2">
    <span class="keyword">if</span>
    <span class="punctuation">(</span>arg<span class="punctuation">)</span>
    <span class="punctuation">{</span>
  </div>
  <div class="code-line line-number" line="3">
    $<span class="punctuation">.</span><span class="function">facebox</span
    ><span class="punctuation">(</span><span class="punctuation">{</span> div<span class="">:</span>
    <span class="string">'#foo'</span>
    <span class="punctuation">}</span><span class="punctuation">)</span>
  </div>
  <div class="code-line line-number" line="4">
    <span class="punctuation">}</span>
  </div>
  <div class="code-line line-number" line="5">
    <span class="punctuation">}</span>
  </div></code
>

Styling

To style the language tokens, you can just copy them from any prismjs compatible ones. Here's a list of themes.

In addition, the following styles should be added for line highlighting and line numbers to work correctly:

pre {
  overflow-x: auto;
}

/**
 * Inspired by gatsby remark prism - https://www.gatsbyjs.com/plugins/gatsby-remark-prismjs/
 * 1. Make the element just wide enough to fit its content.
 * 2. Always fill the visible space in .code-highlight.
 */
.code-highlight {
  float: left; /* 1 */
  min-width: 100%; /* 2 */
}

.code-line {
  display: block;
  padding-left: 16px;
  padding-right: 16px;
  margin-left: -16px;
  margin-right: -16px;
  border-left-width: 4px;
  border-left-color: rgb(31, 41, 55); /* Set code block color */
}

.highlight-line {
  margin-left: -16px;
  margin-right: -16px;
  background-color: rgba(55, 65, 81, 0.5); /* Set highlight bg color */
  border-left-width: 4px;
  border-left-color: rgb(59, 130, 246); /* Set highlight accent border color */
}

.line-number::before {
  display: inline-block;
  width: 1rem;
  text-align: right;
  margin-right: 16px;
  margin-left: -8px;
  color: rgb(156, 163, 175); /* Line number color */
  content: attr(line);
}

Here's the styled output using the prism-night-owl theme:

For more information on styling of language tokens, consult refractor and Prism.

API

rehype().use(rehypePrism, [options])

Syntax highlights pre > code. Under the hood, it uses refractor, which is a virtual version of Prism.

The code language is configured by setting a language-{name} class on the <code> element. You can use any language supported by refractor.

If no language-{name} class is found on a <code> element, it will be skipped.

options

options.ignoreMissing

Type: boolean. Default: false.

By default, if {name} does not correspond to a language supported by refractor an error will be thrown.

If you would like to silently skip <code> elements with invalid languages or support line numbers and line highlighting for code blocks without a specified language, set this option to true.

options.showLineNumbers

Type: boolean. Default: false.

By default, line numbers will only be displayed for code block cells with a meta property that includes 'showLineNumbers'.

If you would like to show line numbers for all code blocks, without specifying the meta property, set this to true.

Note: This will wrongly assign a language class and the class might appear as language-{1,3} or language-showLineNumbers, but allow the language highlighting and line number function to work. An possible approach would be to add a placeholder like unknown so the div will have class="language-unknown"