Resolving “Window is not defined” Error in Next.js SSR

Background

Our development team encountered a critical issue while running the npm run build command in a Next.js server-side rendered (SSR) application. The error message indicated that "window is not defined," pointing to a problem related to server-side rendering.

Problem Statement

When attempting to build the project using the npm script for production (npm run build), the build process failed with an error that specifically mentioned the absence of the "window" object. This issue is common in Next.js applications that utilize server-side rendering, as certain components may attempt to access the "window" object, which is not available on the server side.

Investigation

To identify the root cause of the problem, our development team thoroughly examined the components and dependencies involved in the build process. It was determined that certain components were trying to access the “window” object directly, causing the build to fail.

Solution

To resolve the “window is not defined” error during the build process, we implemented the following solution:

1. Conditional Rendering: We modified the affected components to conditionally check whether the “window” object is defined before attempting to access it. This conditional rendering ensures that the problematic code is only executed on the client side, preventing errors during server-side rendering.

if (typeof window !== "undefined") {
  // Code that relies on the window object
  // ...
}

This simple check ensures that the code within the conditional block is only executed in a client-side context where the “window” object is available.

2. Dynamic Import with Next.js: To handle the SSR-related issues more gracefully, we leveraged Next.js dynamic imports with the ssr: false option. By doing this, we allowed specific components to be loaded dynamically on the client side, avoiding potential conflicts during server-side rendering.

import dynamic from 'next/dynamic';

const DynamicComponent = dynamic(() => import('../path/to/component'), {
  ssr: false,
});

This approach ensures that the designated component is only loaded on the client side, mitigating any issues related to the “window is not defined” error during the build process.

Results: Implementing the above solutions successfully resolved the “window is not defined” error during the npm run build command in our Next.js SSR application. The build process now completes without any issues, and the application functions as expected in both development and production environments.

This case study highlights the importance of understanding the nuances of server-side rendering in Next.js applications and provides a practical solution for mitigating common challenges associated with the “window is not defined” error during the build process.