React Custom Hooks — Reusable Logic Made Easy

useFetch — Data Fetching Hook

function useFetch(url) {
  const [data, setData] = useState(null);
  const [loading, setLoading] = useState(true);
  const [error, setError] = useState(null);
  
  useEffect(() => {
    let cancelled = false;
    setLoading(true);
    fetch(url)
      .then(r => r.json())
      .then(data => { if (!cancelled) setData(data); })
      .catch(err => { if (!cancelled) setError(err); })
      .finally(() => { if (!cancelled) setLoading(false); });
    return () => { cancelled = true; };
  }, [url]);
  
  return { data, loading, error };
}

// Usage
function UserProfile({ userId }) {
  const { data: user, loading, error } = useFetch(`/api/users/${userId}`);
  if (loading) return <Spinner />;
  if (error) return <Error message={error.message} />;
  return <div>{user.name}</div>;
}

useLocalStorage

function useLocalStorage(key, initialValue) {
  const [value, setValue] = useState(() => {
    const stored = localStorage.getItem(key);
    return stored !== null ? JSON.parse(stored) : initialValue;
  });
  
  useEffect(() => {
    localStorage.setItem(key, JSON.stringify(value));
  }, [key, value]);
  
  return [value, setValue];
}

useMediaQuery

function useMediaQuery(query) {
  const [matches, setMatches] = useState(
    () => window.matchMedia(query).matches
  );
  
  useEffect(() => {
    const media = window.matchMedia(query);
    const listener = (e) => setMatches(e.matches);
    media.addEventListener('change', listener);
    return () => media.removeEventListener('change', listener);
  }, [query]);
  
  return matches;
}

// Usage
function Sidebar() {
  const isMobile = useMediaQuery('(max-width: 768px)');
  return isMobile ? <MobileSidebar /> : <DesktopSidebar />;
}

useOnClickOutside

function useOnClickOutside(ref, handler) {
  useEffect(() => {
    function listener(event) {
      if (!ref.current || ref.current.contains(event.target)) return;
      handler(event);
    }
    document.addEventListener('mousedown', listener);
    document.addEventListener('touchstart', listener);
    return () => {
      document.removeEventListener('mousedown', listener);
      document.removeEventListener('touchstart', listener);
    };
  }, [ref, handler]);
}