MDX link routing in Gatsby

In my last article, I wrote about how I was able to parse frontmatter through MDX in Gatsby for a more powerful writing/developer experience. I also mentioned a few remark plugins I brought in-house. Today, I'll walkthrough how I was able to remove three dependencies for just a few lines of code.

Creating links in Markdown is fairly straightfoward:

[Link](https://www.zslabs.com)

With the help of a few plugins, we're able to make these links do a bit more for us automagically:

remark-external-links: Automatically adds target and rel attributes to external links.
remark-relative-links: Rewrites absolute URLs to relative ones.
gatsby-plugin-catch-links: Intercepts local links and replaces their behavior with that of the gatsby-link navigate.

With MDX's ability to override normal DOM elements, I was able to encapsulate the logic from all three of these plugins into a handy snippet:

MarkdownLink.js

import PropTypes from 'prop-types'
import { Link as GatsbyLink } from 'gatsby'
 
// Checks against absolute URLs that share 👇 so we can still pass it along to Gatsby's internal link component
const domainRegex = /http[s]*:\/\/[www.]*YOURDOMAIN\.com[/]?/
// @NOTE We can use a REGEX like this for URLs we want to be treated as external which could be used for Netlify redirects
// /http[s]*:\/\/[www.]*YOURDOMAIN\.com(?!\/i-am-external|\/me-too)[/]?/
 
const MarkdownLink = ({ href, ...rest }) => {
  const sameDomain = domainRegex.test(href)
 
  if (sameDomain) {
    href = href.replace(domainRegex, '/')
  }
 
  if (href.startsWith('/')) {
    return <GatsbyLink data-link-internal to={href} {...rest} />
  }
 
  // Treat urls that aren't web protocols as "normal" links
  if (!href.startsWith('http')) {
    return <a href={href} {...rest} /> // eslint-disable-line jsx-a11y/anchor-has-content
  }
 
  return <a data-link-external href={href} rel="nofollow" {...rest} />
}
 
MarkdownLink.propTypes = {
  href: PropTypes.string.isRequired,
}
 
export default MarkdownLink

This can then be passed into <MDXProvider /> to override default links:

Article.js

import { MDXProvider } from '@mdx-js/react'
import { MDXRenderer } from 'gatsby-plugin-mdx'
 
import MarkdownLink from '../components/MarkdownLink'
 
const Article = ({ frontmatter, body }) => (
  <MDXProvider
    components={[
      {
        a: (props) => <MarkdownLink {...props} />,
      },
    ]}
  >
    <div>
      <h1>{frontmatter.title}</h1>
 
      <MDXRenderer>{body}</MDXRenderer>
    </div>
  </MDXProvider>
)

Since our Markdown links are now powered by a React component, we can apply any other special formatting or logic as needed. Take a look at this one and others I've added to my own site in my shortcodes file. 🎉