React timer

const PomView = () => {
  const [timer, setTimer] = useState(1500); // 25 minutes
  const [start, setStart] = useState(false);
  const firstStart = useRef(true);
  const tick = useRef(); // <-- React ref

  useEffect(() => {
    if (firstStart.current) {
      firstStart.current = !firstStart.current;
      return;
    }

    if (start) {
      tick.current = setInterval(() => {
        setTimer((timer) => timer - 1);
      }, 1000);
    } else {
      clearInterval(tick.current);
    }

    return () => clearInterval(tick.current);
  }, [start]);
};