React usePrevious Custom Hook #hooks

usePrevious-hook.ts

const usePrevious = <T>(value: T): T => {
  // The ref object is a generic container whose current property is mutable ...
  // ... and can hold any value, similar to an instance property on a class
  const ref: any = useRef<T>();

  // Store current value in ref
  useEffect(() => {
    ref.current = value;
  }, [value]); // Only re-run if value changes

  // Return previous value (happens before update in useEffect above)
  return ref.current;
};