In your page components, you can execute code only in the server-side or on the client-side, but checking the window property.
This property is only existing inside the browser, so you can check
if (typeof window === 'undefined') {
}
and add the server-side code in that block.
Similarly, you can execute client-side code only by checking
if (typeof window !== 'undefined') {
}
JS Tip: We use the
typeofoperator here because we can’t detect a value to be undefined in other ways. We can’t doif (window === undefined)because we’d get a “window is not defined” runtime error
Next.js, as a build-time optimization, also removes the code that uses those checks from bundles. A client-side bundle will not include the content wrapped into a if (typeof window === 'undefined') {} block.
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