탭전환 여부를 감지하는 hook

  useEffect(() => {
    const onFocus = () => console.log('focus On');
    if (typeof window !== 'undefined' && window.addEventListener) {
      window.addEventListener('focus', onFocus, false);
    }

    return () => {
      window.removeEventListener('focus', onFocus);
    };
  }, [])