Missing useEffect Cleanup

useEffect with subscriptions/timers but no cleanup

warningReliabilitymissing-useeffect-cleanup

Why this matters

Without cleanup, subscriptions and timers keep running after the component unmounts. This causes memory leaks, stale state updates, and 'can't update unmounted component' errors.

✗ Bad

useEffect(() => {
  const interval = setInterval(() => {
    fetchNotifications();
  }, 5000);
  // No cleanup — interval runs forever
}, []);

✓ Good

useEffect(() => {
  const interval = setInterval(() => {
    fetchNotifications();
  }, 5000);

  return () => clearInterval(interval);
}, []);

How to fix

Return a cleanup function from every useEffect that creates subscriptions, timers, event listeners, or WebSocket connections.

All rules