mjml-react does not seem to work in NextJS

[bduff9]

Hello! I have been using mjml for quite some time and recently started a new project with nextJS 13 and this library. Unfortunately, something seems to be going wrong and I get an empty MJML string every time when I run renderToMjml:

<mjml owa="desktop"><mj-head></mj-head><mj-body></mj-body></mjml>

I was able to recreate a minimal example only using the latest version of next and the latest version of this library here:
https://codesandbox.io/p/sandbox/nextjs-13-mjml-4yktfz

Any idea on why this is happening or how to fix? Thank you!

[emmclaughlin]

Hi @bduff9 , thank you for reporting the problem. I have not worked with nextJS 13 too much, so I am not immediately sure what is going on here. I did narrow it down a bit more though. I tried to defined:

  const mjmlContent = (
    <MjmlSection>
      <MjmlColumn>
        <MjmlText>Hello world</MjmlText>
      </MjmlColumn>
    </MjmlSection>
  );

  const htmlContent = (
    <div>
      <p>
        <a>Hello world</a>
      </p>
    </div>
  );

  const mjmlStaticMarkup = ReactDOMServer.renderToStaticMarkup(mjmlContent);
  const htmlStaticMarkup = ReactDOMServer.renderToStaticMarkup(htmlContent);

and got back

mjmlStaticMarkup -> <mj-section></mj-section>
htmlStaticMarkup -> <div><p><a>Hello world</a></p></div>

So something is going on with the MjmlReact components that is causing renderToStaticMarkup (what renderToMjml uses under the hood) to not work in your example. I suspect it could be the React version, but I will have to dig a bit deeper. Just wanted to provide a quick update in case this context is helpful to you.

[emmclaughlin]

I tracked this down to a change in renderToStaticMarkup that I think started in react-dom v18 (I confirmed the error doesn't exist in react-dom v17). The change made was to change the functionality of how custom elements are handled, and it seems that the children prop is getting skipped for custom elements at this step.

The quickest solution to your issue will be either:

• use React 17
• use a different method for converting JSX to a string

As far as the long term solution, I am not certain yet. It seems like the naming of the mjml elements (e.g. mj-column, mj-head) clash with the naming structure of custom elements, as the check for custom element is just if there is a hyphen. I see our options as either:

• Adjust mjml-react so that the naming does not clash with custom elements and add the hyphen into the string after calling renderToStaticMarkup
  • This is not ideal because we are relying on string manipulation to post process the string, which is susceptible to errors
• Push a commit to react that allows it to differentiate a true custom element from an mjml element
  • I don't currently know if there is a way to do this
• Implement our own method for converting the jsx containing mjml to a string
  • The most robust option, but also the most work

[bduff9]

@emmclaughlin Thanks for looking into this. Unfortunately, downgrading to React 17 is not an option. I believe Next 13 requires React 18 but even if it doesn't, we use several React 18 features such as Suspense.

As far as using a different method to convert JSX to a string, do you have any suggestions for that? It's not an area I have looked at much previously.

[emmclaughlin]

I have not looked into it much. From a quick search here are some potential options to try:

• https://www.npmjs.com/package/react-element-to-jsx-string
• https://www.npmjs.com/package/@sequencemedia/react-render
• https://www.npmjs.com/package/jsx-to-string

[bduff9]

@emmclaughlin Thanks, I saw those too. Unfortunately, the first and third options only render the JSX string, not the HTML markup. The middle option just uses renderToStaticMarkup like mjml-react so that's a no-go too. I'll keep looking though, would love to use this library. Thanks again.

[emmclaughlin]

@bduff9 I was worried that would be the case. I will keep looking to see if there is any other quick workaround that can unblock you here and let you know if I find anything

[Palmik]

For now I have solved this by using pnpm add react-dom-17@npm:react-dom@^17.0.0. Likely you only ever render the emails server side, so there's no client-side bloat.

Also, if you are using app router like me (I have a simple previewer app for MJML react), then you want:

module.exports = {
  experimental: {
    serverComponentsExternalPackages: ['mjml']
  }
}

In your next.config.js, otherwise you get weird errors about uglify imports: vercel/next.js#50042

[emmclaughlin]

Update from the React team: facebook/react#27403 (comment)

Sounds like it should be fixed in the next release 🙌

[emmclaughlin]

Closing this issue as we have tested mjml-react with the latest React canary builds and their fix is sufficient to reconcile this issue.