Next.js, fix the `module not found` error

While doing some sanitization on a variable in Next.js I ran into this weird problem:

Module not found: Error: Can't resolve 'net'

You might have some variation of it, which says a core Node.js module is missing.

Do NOT npm install net or anything like that. If you already tried, run npm uninstall on those modules.

The problem is this: Next.js is trying to run backend code in the frontend.

In my case it was the DOMPurify library. I was using it inside the component, but instead I had to use it in the getStaticProps() method.

That method runs at build time in the Node environment, where that library expected to be ran into.