feat: Attach export to MDXContent?

[domdomegg]

Not sure whether this is in scope for this plugin - feel free to close if so.

I'm hoping to use this plugin with Next.js so that I can insert a header component using the frontmatter content. I think I currently can't access it from _app.tsx, where this is currently rendered. I could access it by adding something to every .mdx file, but this adds overhead to writing pages that I want to avoid.

To fix this, I was hoping this plugin could add it to the component itself, e.g. so rather than:

export const frontmatter = {
  hello: 'frontmatter'
}

export default function MDXContent() {
  return <p>Rest of document</p>
}

It outputs:

export default function MDXContent() {
  return <p>Rest of document</p>
}

MDXContent.frontmatter = {
  hello: 'frontmatter'
}

This is somewhat similar to what's described in https://www.josephrex.me/frontmatter-with-nextjs-and-mdx/ - although the actual component would be in _app.tsx.

---

This is roughly what I had in mind for my _app.tsx:

import '../styles/globals.css';
import type { AppProps } from 'next/app';

const App: React.FC<AppProps> = ({ Component, pageProps }: AppProps) => {
  if (Component.displayName === 'MDXContent') {
    return (
      <>
        <Header frontmatter={Component.frontmattter} />
        <div className="max-w-sm md:max-w-2xl mx-auto px-8 py-12 md:my-24 prose animate-fade-up">
          <Component {...pageProps} />
        </div>
      </>
    );
  }

  return <Component {...pageProps} />;
};

export default App;

[remcohaszing]

I suggest you take a look at recma-nextjs-static-props.

[domdomegg]

Thanks! I couldn't quite figure out how to get that one working, so I've done it a hacky way in recma-mdx-frontmatter. Closing this given there seem multiple ways to achieve what I wanted without this feature request.

[remcohaszing]

I’m glad you found a solution to your problem. Still, could you elaborate what wasn’t working for you with recma-nextjs-static-props?

[domdomegg]

I think I didn't quite see how to but the bits together, at least on my inital look at it. I haven't given it another shot, but now I think it would roughly be:

• use remark-mdx-frontmatter to export the frontmatter object
• use recma-nextjs-static-props to add the frontmatter object to get static props
• use pageProps in Next.js to access these static props in _app.tsx (although caveat I'm not sure this works - there seems to be a warning "App does not support Next.js Data Fetching methods like getStaticProps or getServerSideProps.")

Is that right?

I think the thing that would have made me more likely to take this route would be a more complete documentation example with an _app.tsx (not saying you need to do this - appreciate it's just one use case, and don't mean to shift the burden on you when it's something I could maybe have figured out).

(also as for timings - I played around with this yesterday, and only saw your comment suggesting recma-nextjs-static-props after I had created my separate recma plugin)

[domdomegg]

Out of interest, I ended up giving implementing this a go. In short, yes the above works:

domdomegg/domdomegg.github.io@497ec45

I think using getStaticProps seems to change the developer experience a little. Live reload doesn't work quite as nicely: instead of instantly updating the right part, whenever any change is made the whole page reloads. I think this difference is minor though and someone smarter than me can probably figure out how to make it work with the above method.

[remcohaszing]

The distinction between getStaticProps vs a property on MDXContent you’re describing is interesting. Thanks for sharing.

---

I see some bugs in recma-mdx-frontmatter:

• You’re using gray-matter, which uses js-yaml under the hood, which has some parsing bugs. I strongly recommend using yaml instead.
• pojoToEstree doesn’t support several types that js-yaml may yield, including negative numbers and Date. I suggest you take a look at estree-util-value-to-estree.

[domdomegg]

Both good suggestions, I will look into them. I really appreciate the time you've put into reviewing the code and the kind way you've delivered the feedback!

I'm initially hesitant to reimplement parts of gray-matter, given it seems widely used and recommended in this space. I suspect trying to do so myself would likely introduce more bugs rather than less! But I see in jonschlinkert/gray-matter#147 it may be a bit stuck.

I agree pojoToEstree feels a little rough around the edges. I'll take a look at estree-util-value-to-estree. I was initially spooked by it being ESM, but I'll give it a revisit (and I know I might seem slightly crazy for still trying to maintain CJS - but it makes sense for where I want to use some of my packages: and for standardisation reasons it's nice to have all my packages use similar build processes etc.).