Why Am I Getting a 'Window is not defined' Error in My Next.js App?

"Window is not defined" Error in Next.js React App

One common challenge encountered when building React applications with Next.js is the inability to access the window object because Next.js utilizes server-side rendering by default. This absence of the window object can lead to errors like "ReferenceError: window is not defined."

A common pitfall is attempting to utilize the window object during the component lifecycle methods such as componentWillMount. However, since these methods are executed on the server, the browser's window object is unavailable during this phase.

A straightforward solution to this problem is using a conditional check to verify if the window object is defined. This ensures that the code dependent on the window object is only executed on the client-side, where it has access to it:

if (typeof window !== "undefined") {
  // Client-side-only code
}

By incorporating this conditional check, your code will gracefully handle the absence of the window object during server-side rendering.

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