When is the cleanup function triggered when using useEffect hook with dependencies?

Question

I\'m using a useEffect to show a UI Loading... but only after 250ms. It works ... but I really don\'t understand why and specially how and when useEffect invokes the returned fu

Answer 1

As per the react documentation,

Cleaning up an effect

The clean-up function runs before the component is removed from the UI to prevent memory leaks. Additionally, if a component renders multiple times (as they typically do), the previous effect is cleaned up before executing the next effect.

Timing of effects

React will always flush a previous render’s effects before starting a new update.

As per my understanding from both the quotes, cleanup runs after the effect is applied and before the component is unmounted (removed from UI).