Next.JS Error: No router instance found

· May 29, 2021

I ran into a stupid problem I created for myself. And then I solved and that made me realize a thing about Next.JS and the server side rendering features of this framework.

I wanted to share my failures and solution to the problems I created here.

I have a page that is server-side rendered, since I’m the getServerSideProps.

One of the components on the page, reach out and grabs the router:

import { useRouter } from 'next/router';

const Header = () => {
  const router = useRouter();

And I then added a click-handler like this:

<div onClick={router.push('/')}>

And it blew up, with a very nice, but ultimately not helpful error message:

Error: No router instance found. you should only use “next/router” inside the client side of your app.

So this error even has an page on the Next.JS site and it’s helpfully trying to tell me that I’m using the router on the server-side. It also sent me down the wrong route (hehe sorry) to try to create the routing in the useEffect hook.

When in fact the solution was much easier

The solution - declare the function. Don’t call it

As I’ve written the function now, the router.push('/')will be called on server-side rendering, since I’m invoking the router.push But that’s not what I want. I want it to be called when the user clicks. This should be done like this:

<div onClick={() => router.push('/')}>
 ... stuff

And I had one of those …. BUT OF COURSE.

But then I realized how much sense it made - the server side rendered version should just render the function to be executed when the user clicks the div. Not execute the function. A bit like the difference of declaring a callback and actually calling it.

A simple slip-up but the reflection made me think about what server side rendering is and I learned some more. WIN.

I hope you found this useful.

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