Solving the ‘window is not defined’ Error in Next.js

Next.js is a popular framework, which has gained a lot of traction for its server-side rendering capabilities and seamless integration with the React library. During development in Next.js, you may encounter some unique challenges, such as the ‘window is not defined’ error.

In this article, we will discuss this error in depth and provide solutions to overcome it.

In Next.js, server-side rendering (SSR) is a key feature that allows for improved performance and search engine optimization (SEO). However, this can also lead to some issues, particularly when trying to access the window object.

The ‘window is not defined’ error occurs because the window object is only available in the browser environment, while Next.js’s SSR executes code on the server-side, where the window object does not exist.

Why the ‘Window is not defined’ error is caused?

In a typical React application, developers often use the window object to access browser-specific functionalities like the Document Object Model (DOM), user agent, and screen dimensions. However, when using Next.js for server-side rendering, the code is executed on the server, where the window object is not available, leading to the this error.

How Next.js handles server-side rendering

Next.js improves the performance of React applications by rendering the initial HTML on the server and then sending it to the client. This approach ensures that the user sees the content quickly, even before the JavaScript is fully loaded in the application. Server-side rendering is beneficial for SEO, as search engine crawlers can more easily index the content.

How to Solve ‘window is not defined’ error in Next.js

There are several methods to address the this error in Next.js applications:

Method 1 – Using useEffect hook

The useEffect hook allows to perform side effects, such as accessing the window object, after the component has been already rendered. By doing this, we ensure that the code which needs the window object is only executed on the client-side.

Example use-case:

import React, { useEffect } from 'react';

const MyComponent = () => {
  useEffect(() => {
    const windowHeight = window.innerHeight;
    // Perform actions with windowHeight
  }, []);

  return (
    // Your component JSX
  );
};

Method 2 – By Dynamic import

Next.js supports dynamic imports, which allow to load modules only on the client side. By using the dynamic function from the ‘next/dynamic‘ package, you can import a module that depends on the window object and ensure it only runs on the client side.

Example:

import dynamic from 'next/dynamic';

const ComponentWithWindow = dynamic(
  () => import('./ComponentWithWindow'),
  { ssr: false }
);

const MyComponent = () => {
  return (
    <div>
      <ComponentWithWindow />
    </div>
  );
};

Method 3 – Conditional rendering

Another approach to handling the window error is to by using conditional rendering. By checking whether the window object exists before using it, you can prevent the error from occurring during server-side rendering.

Example:

const MyComponent = () => {
  const isBrowser = typeof window !== 'undefined';

  return (
    <div>
      {isBrowser && (
        // Your component JSX that uses the window object
      )}
    </div>
  );
};

Conclusion

Next.js is an incredibly framework that offers server-side rendering to improve the performance and SEO of React applications. But it can also introduce some challenges, such as the window not defined error. By using the solutions provided in this article, including the useEffect hook, dynamic imports, and conditional rendering, you can successfully overcome this error and create seamless Next.js applications.