USE EFFECT

[hello2jolee]

useEffect == componentWillUnmount, componentDidMount, componentWillUpdate

[hello2jolee]

useEffect(() => {
    if (element.current) { // componentDidMount → add an effect
      element.current.addEventListener("click", onClick);
    }
    return () => element.current.removeEventListener("click", onClick); // componentWillUnmount → remove an effect (clean up after myself)
  });