Here’s how to fix the “referenceerror: window is not defined” error that you might have in Node.js or with a tool like Next.js.

window is an object that’s made available by the browser, and it’s not available in a server-side JavaScript environment.

I describe the window object is details in my extensive DOM Document Object Model guide.

With Node.js in particular there’s no way to workaround the problem - you must find the particular place where window is used, and revisit the code to figure out why you are accessing the window object.

You are running frontend code in a backend environment.

In Next.js you can fix this problem by wrapping the code you run in a conditional.

The code might be running in both situations - frontend, when you navigate to a page using a link, and server-side if you require server-side into your page, for example by running getServerSideProps().

In this case, you can limit the reference into a conditional that checks if the window object is available, like this:

if (typeof window !== 'undefined') {
  //here `window` is available
}

And this will fix your problem, since you only run anything inside the conditional in a browser environment.

Lessons in this unit:

0:	Introduction
1:	Fix Node.js imports types errors in VS Code
2:	▶︎ referenceerror: window is not defined, how to solve
3:	Use the Chrome DevTools to debug a Node.js app
4:	Error handling in Node.js
5:	How to solve the `util.pump is not a function` error in Node.js