Next.js & MDX w/ code highlighting

A walkthrough on how to configure Next.js to render MDX files with code highlighting.

I use this as a quick way to write documentation for small projects. It can also be useful for creating nicely formatted PDFs with code highlighting built in.

Let's get started!

Using MDX

Assuming you have a fresh Next.js project - begin by installing the Next.js MDX package:

npm install @next/mdx @mdx-js/loader

In next.config.js, configure Next.js to handle MDX files:

// next.config.js
const withMDX = require('@next/mdx')({
    extension: /\.mdx?$/,
});

module.exports = withMDX({
    pageExtensions: ['js', 'jsx', 'mdx'],
});

This means we can now create a MDX file in the pages directory and Next will magically do the routing and rendering for us. Let's try it. In the pages folder, create a new onions.mdx file:

# Onions

Layers. Onions have layers. Ogres have layers. Onions have layers. You get it? We both have layers.

Oh, you both have layers. Oh. You know, not everybody like onions.

```js
const year = "2001";
const movie = "Shrek";

console.log(`${movie}, ${year}`);

Run the project with npm run dev and navigate to /onions to see the rendered MDX page:

Syntax highlighting

Currently our code block has no highlighting - let's change that!

Install the remark-prism package. Then update next.config.js to include the plugin:

// next.config.js
const withMDX = require("@next/mdx")({
  extension: /\.mdx?$/,
  options: {
    remarkPlugins: [require("remark-prism")],
  },
});

module.exports = withMDX({
  pageExtensions: ["js", "jsx", "mdx"],
});

Then find a Prism highlighting theme to use - it's essentially a CSS file. As a starting point, check out this prism-theme repository for a list of options.

I'm a fan of the Dracular theme. I will add it to the project by creating a _document.js file and linking to the stylesheet in the head:

import Document, { Html, Head, Main, NextScript } from "next/document";

class MyDocument extends Document {
  render() {
    return (
      <Html>
        <Head>
          <link
            rel="stylesheet"
            href="https://unpkg.com/dracula-prism/dist/css/dracula-prism.css"
          ></link>
        </Head>
        <body>
          <Main />
          <NextScript />
        </body>
      </Html>
    );
  }
}

export default MyDocument;

Restart the dev server. The code block should now be highlighted!

Styling with Water.css

As an added bonus, I like to add a few quick styles. Water.css provides a great default stylesheet and saves us having to write our own. This can be added to the _document.js file as a stylesheet:

<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/water.css@2/out/dark.css"></link>

By default, the generated Next.js styles/globals.css file sets all padding and margin to zero. I also remove these rules to get some padding and margin back.

The end result should look something like:

🎉

Print as a PDF

Aside from hosting the project and sharing the URL - you can also print the page and set the destination as a PDF. This will produce a nicely formatted PDF file to share with others.