Memory Leak - Component Doesn't Clean Up Resources

1. useEffect without cleanup function for event listeners, intervals, subscriptions
2. Setting state on unmounted component
3. Global state not being cleared when component unmounts
4. WebSocket or fetch requests not aborted on cleanup
5. Timer/interval not cleared in cleanup

Always return cleanup from useEffect: useEffect(() => { const timer = setInterval(...); return () => clearInterval(timer); }, [])

Abort fetch requests: const controller = new AbortController(); fetch(url, { signal: controller.signal }); return () => controller.abort()

Remove event listeners: addEventListener then removeEventListener in cleanup

Check for 'Can't perform a React state update on an unmounted component' warnings