Question

An AI wrote this React Native countdown component for a limited-time offer. It works on screen, but after navigating between offers a few times, performance degrades and you see the timer 'tick' firing multiple times per second and warnings about setting state on an unmounted component. What's wrong and how would you fix it?

1function Countdown({ endsAt }) {2  const [left, setLeft] = useState(endsAt - Date.now());3  useEffect(() => {4    setInterval(() => {5      setLeft(endsAt - Date.now());6    }, 1000);7  });8  return <Text>{Math.max(0, Math.floor(left / 1000))}s</Text>;9}