Why React useState with functional update form is needed?

Question

I\'m reading React Hook documentation about functional updates and see this quote:

The ”+” and ”-” buttons use the functional form, because the updat

Answer 1

Another use case for using functional updates with setState - requestAnimationFrame with react hooks. Detailed information is available here - https://css-tricks.com/using-requestanimationframe-with-react-hooks/

In summary, handler for requestAnimationFrame gets called frequently resulting in incorrect count value, when you do setCount(count+delta). On the other hand, using setCount(prevCount => prevCount + delta) yields correct value.