What Is a Useeffect Cleanup Function?

In other words, the useEffect cleanup functions run asynchronously - for example, if the component is unmounting, the cleanup runs after the screen has been updated. Additionally, React 17 will always execute all effect cleanup functions (for all components) before it runs any new effects.

Why is useEffect cleanup called?

In short, the reason is because such design protects against stale data and update bugs. The useEffect hook in React is designed to handle both the initial render and any subsequent renders (here's more about it). Effects are controlled via their dependencies, not by the lifecycle of the component that uses them.

What is cleanup in react?

React performs the cleanup when the component unmounts. However, as we learned earlier, effects run for every render and not just once. This is why React also cleans up effects from the previous render before running the effects next time.