useEffect

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When not to use

If you can calculate something during render, you don’t need an Effect.
To cache expensive calculations, add useMemo instead of useEffect.
To reset the state of an entire component tree, pass a different key to it.
To reset a particular bit of state in response to a prop change, set it during rendering.
Code that runs because a component was displayed should be in Effects, the rest should be in events.
If you need to update the state of several components, it’s better to do it during a single event.
Whenever you try to synchronize state variables in different components, consider lifting state up.
You can fetch data with Effects, but you need to implement cleanup to avoid race conditions.