React hooks useEffect only on update?

Question

If we want to restrict useEffect to run only when the component mounts, we can add second parameter of useEffect with [].

Answer 1

You can get around it by setting the state to a non-boolean initial value (like a null value) :

  const [isCartOpen,setCartOpen] = useState(null);
  const [checkout,setCheckout] = useState({});

  useEffect(() => {

    // check to see if its the initial state
    if( isCartOpen === null ){

      // first load, set cart to real initial state, after load
      setCartOpen( false );
    }else if(isCartOpen === false){

      // normal on update callback logic
      setCartOpen( true );
    }
  }, [checkout]);