useIsomorphicLayoutEffect

The React documentation says about useLayoutEffect:

The signature is identical to useEffect, but it fires synchronously after all DOM mutations.

That means this hook is a browser hook. But React code could be generated from the server without the Window API.

If you're using NextJS, you'll have this error message:

Warning: useLayoutEffect does nothing on the server, because its effect cannot be encoded into the server renderer's output format. This will lead to a mismatch between the initial, non-hydrated UI and the intended UI. To avoid this, useLayoutEffect should only be used in components that render exclusively on the client. See https://reactjs.org/link/uselayouteffect-ssr for common fixes.

This hook fixes this problem by switching between useEffect and useLayoutEffect following the execution envirnment.

export default function Component() {
  useIsomorphicLayoutEffect(() => {
    console.log(
      "In the browser, I'm an `useLayoutEffect`, but in SSR, I'm an `useEffect`.",
    )
  }, [])

  return <p>Hello, world</p>
}