Static Pages Without JavaScript Inside Next.js

Next.js isn’t a pure HTML static site generator since JavaScript is required for many interactive parts of the site.

Most people that visit your site stay there for one page, so we don’t have to incur a cost of the entire JavaScript runtime.

That said, if you have a page that doesn’t require JavaScript wouldn’t it be great if you could just remove it? You can do that thanks to a experimental Next.js feature.

{% src=“experimental-feature.webp” alt=“Experimental feature for removing client-side JavaScript in production” %}

I created a typical Next.js app using npx create-next-app --typescript and removed some of the cruft, so we’re left with basic styles.

{% src=“network-with-javascript.webp” alt=“Network tab JavaScript bundle size” %}

I ran npm run build, and after npm start we’re greeted with a bundle size of 71.89 kB. If we look inside the Inspector we can see the JavaScript used to run this single page.

{% src=“inspector-with-javascript.webp” alt=“Inspector tab with JavaScript” %}

There’s no JavaScript required on this page, so let’s remove it. This requires us to export a config inside a page with the experimental unstable_runtimeJS option set to false.

index.tsx
export const config = {
  unstable_runtimeJS: false
}

After we build and open the page we can see the size is just 3 kB since there’s no JavaScript, and inside the Inspector there’s only static HTML.

{% src=“network-without-javascript.webp” alt=“Network tab without JavaScript” %}

{% src=“inspector-without-javascript.webp” alt=“Inspector tab without JavaScript” %}

If you have other pages everything works fine. It’s just going to download JavaScript when it’s required which means we don’t get preloading.

Conclusion

Keep in mind this is experimental and only works in production, so if you’re in development everything might seem to work but remember the JavaScript won’t work in production.

You can’t execute JavaScript on the page without injecting custom <script> tags into the rendered HTML as mentioned in the pull request, but for most static pages it works great.

If you’re interested in reducing the bundle size of your Next.js site for parts where you do use JavaScript, I wrote Reduce Next.js Bundle Size by Half.

Thanks for reading! 🏄‍♀️

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