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React In MDX (In React)
2019-03-31
Migrating from rehype-react to gatsby-mdx, and a few lessons learned along the way.
true

import ZoomImage from 'components/ZoomImage'; import XA from 'components/ExternalAnchor';

import lake from './lake.jpg'; import lakeZoom from './lake-zoom.jpg';

A bit over a year ago, I wrote about why I was so excited for React in Markdown. (I'm still excited about it, by the way!) At the end of that post, I included a note about an interesting proposal for a .mdx format by ZEIT's Guillermo Rauch, which had been published just a day earlier. Fast forward to today and MDX has over 6,000 stars on GitHub. Out of all the libraries in this space, MDX seems to be the clear winner.

Old and busted: rehype-react

In addition to being widely supported, it has a much better mental model than my previous approach to React in Markdown, which used rehype-react and had some ugly caveats.

For one, I couldn't figure out a good way to include only a certain subset of components in a certain blog post. (I made a note to myself to try and figure this out but I never did.) Every single component (even the heavy ones that include libraries like Three.js) gets included every single blog post, regardless of whether not they are all needed. Not ideal.

This approach also requires that you pass all props to your embedded components as strings. The components I need for this blog are all fairly simple so this never was a huge issue, but if I wanted to do anything more complex this would quickly become a deal-breaker.

All this to say, React in Markdown is here to stay. rehype-react, not so much (at least for me). I'd been following MDX for some time, as well as gatsby-mdx, which makes it easy to consume MDX from a Gatsby blog. I finally had some time after wrapping up a few projects (1, 2) and decided to bite the bullet and give gatsby-mdx a try. A few weeks later, I'm back up and running (this page is MDX!) and on the whole, a total convert! Here are a few things I learned along the way.

New hotness: gatsby-mdx

I took the opportunity while updating to gatsby-mdx to also refactor a fair amount of this blog. That being case, the diff is fairly gnarly. After all, I initially wrote this site not long after learning React itself, and by now I've been writing React professionally for over a year. Still, I'll call out some of the steps that might be useful for someone else getting started with gatsby-mdx.

First, install your dependencies:

npm i gatsby-mdx @mdx-js/mdx @mdx-js/tag

Then, add gatsby-mdx to your gatsby-config.js:

module.exports = {
  plugins: [
    {
      resolve: 'gatsby-mdx',
      options: {
        extensions: ['.mdx'],
        gatsbyRemarkPlugins: [
          // more on this later
        ]
      }
    }
  ]
};

Then, add a .mdx file to src/pages and you're off to the races! For this example, I'll use ZoomImage, like I did in my previous post:

---
title: "ZoomImage Example"
date: "2019-03-31"
---
import ZoomImage from 'components/ZoomImage';

import lake from './lake.jpg';
import lakeZoom from './lake-zoom.jpg';

<ZoomImage src={lake} zoomSrc={lakeZoom} caption='Lake 22, WA' />

And here's what it looks like:

Some gotchas

gatsby-mdx 'just works' (usually).

On the whole, the assumptions made by the library are sane ones. But once in a while, I found myself fighting against the library to maintain the flow of data in the standard 'Gatsby-ish' way. Here are a few examples of things that took some figuring out.

Configuring gatsby-mdx

In order to include components in your MDX files, you'll need to tell gatsby-mdx where to look. All of my components are in src/components, so I use the following configuration in gatsby-node.js:

exports.onCreateWebpackConfig = ({ actions }) => {
  actions.setWebpackConfig({
    resolve: {
      modules: [path.resolve(__dirname, 'src'), 'node_modules']
    }
  });
};

Then in my MDX, I import like so:

import Foo from 'components/Foo';

You'd think this would be at the top of most gatsby-mdx tutorials but it took me a bit of digging to figure out.

gatsbyRemarkPlugins

If you already use Markdown in your Gatsby blog, it's likely that you use gatsby-transformer-remark. gatsby-mdx is a full replacement for gatsby-transformer-remark (unless you opt to use them both, for reasons I'm unsure of). This means that you'll need to modify your gatsby-config.js to account for this.

gatsby-mdx accepts a configuration object, which has an option for gatsbyRemarkPlugins. Mine looks like this:

{
  resolve: 'gatsby-mdx',
  options: {
    gatsbyRemarkPlugins: [
      { resolve: 'gatsby-remark-autolink-headers' },
      { resolve: 'gatsby-remark-prismjs' },
      { resolve: 'gatsby-remark-smartypants' }
    ]
  }
}

I've read that some gatsby-remark plugins won't work out of the box with gatsby-mdx, but so far I haven't run into any issues.

Programmatically rendering MDX

By default, gatsby-mdx will render your MDX in place. As shown in the example above, you can place a foo.mdx file in src/pages, and it'll be detected and rendered at /foo without any further configuration. This is great for getting up and running, but this doesn't completely map to the way that I use MDX in my app. I typically want my MDX files to be wrapped in a layout component, which might display the title, date, and other metadata about the post, as well as common styling.

In order to get access to your MDX files programmatically, you'll need to modify your gatsby-node.js to look something like this:

const path = require('path');
const { createFilePath } = require('gatsby-source-filesystem');

exports.createPages = ({ graphql, actions }) => {
  const { createPage } = actions;

  return new Promise((resolve, reject) => {
    graphql(`
      {
        allMdx {
          edges {
            node {
              fields {
                slug
                type
              }
            }
          }
        }
      }
    `).then(result => {
      if (result.errors) {
        console.error(result.errors);
        reject(result.errors);
      }

      result.data.allMdx.edges.forEach(({ node }) => {
        createPage({
          path: node.fields.slug,
          component: path.resolve('./src/templates/post.js'),
          context: {
            // Data passed to context is available in page queries as GraphQL variables.
            slug: node.fields.slug
          }
        });
      });
      resolve();
    });
  });
};

Then, in src/templates/post.js (or wherever you specified as your component path above), query via the slug we passed above:

import { graphql } from 'gatsby';

export const query = graphql`
  query($slug: String!) {
    mdx(fields: { slug: { eq: $slug } }) {
      frontmatter {
        title
        date
      }
      code {
        body
      }
    }
  }
`;

And now your component should have access to props.data.mdx, with all of the fields passed above:

import React from 'react';
import { MDXRenderer } from 'gatsby-mdx

import Layout from './components/Layout';

const PostTemplate = ({ data }) => {
  const { frontmatter, code } = data.mdx;

  return (
    <Layout>
      <h1>{frontmatter.title}</h1>
      <MDXRenderer>{code.body}</MDXRenderer>
      <span>{frontmatter.date}</span>
    </Layout>
  );
};

Note here that we're passing props.data.mdx.code.body to MDXRenderer, which is what renderers the compiled MDX content.

Passing your data around like this is certainly more tedious than letting gatsby-mdx render your content in place, but I find that this approach is necessary for anything other than toy examples.

File imports

I've yet to figure out a completely ergonomic approach to including relative links to files, especially when passing to components as props. There seems to be a working example in the gatsby-mdx docs showing how to use gatsby-remark-images, but this doesn't work with the custom ZoomImage component I use for image embeds. Previously, I came up with a hacky approach to this that worked with my previous rehype-react setup, but it included a silly Hidden component which was required for webpack to update the file path from a relative one to the published public directory. It worked, but was certainly not ideal.

The solution I landed on is to simply import any necessary files at the top of my MDX file, like so:

import foo from './foo.jpg';

Then, later on, you can use it:

<ZoomImage src={foo} />

The path to foo will be correctly updated to the public directory:

/static/foo-02dc7c71ecb7ee41bfaa345303af6736.jpg

Ideally, I would like to be able to pass the path directly to my component (<ZoomImage src="foo.jpg" />) and have webpack do its magic, but for now, my approach works just fine.

Onward!

MDX is young. gatsby-mdx even moreso.

Things will continue to change (and break, probably), but I'm so happy that there's a growing community of developers working to improve the tooling and ergonomics writing Gatsby web applications. Special thanks to Christopher Biscardi and the rest of the maintainers of gatsby-mdx for their hard work on such a useful and pleasant tool.

Here are some other resources if you'd like to learn more about MDX:

  • gatsby-mdx documentation
  • Building a Video Blog with Gatsby and Markdown on scotch.io
  • What is MDX by Kent C. Dodds

Thanks for reading!

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