React Hooks

Priority: P1 (OPERATIONAL)

Effective usage of React Hooks.

Implementation Guidelines

• Rules: Top-level only. Only in React functions.
• useEffect: Sync with external systems ONLY. Cleanup required.
• useRef: Mutable state without re-renders (DOM, timers, tracking).
• useMemo/Callback: Measure first. Use for stable refs or heavy computation.
• Dependencies: Exhaustive deps always. Fix logic, don't disable linter.
• Custom Hooks: Extract shared logic. Prefix use*.
• Refs as Escape Hatch: Access imperative APIs (focus, scroll).
• Stability: Use useLatest pattern (ref) for event handlers to avoid dependency changes.
• Concurrency: useTransition / useDeferredValue for non-blocking UI updates.
• Initialization: Lazy state useState(() => expensive()).

Anti-Patterns

• No Effects for Data Flow: Derive state in render.
• No Missing Deps: Causes stale closures.
• No Complex Effects: Split into multiple simple effects.
• No Oversubscription: Check why-did-you-render.

Code

// Custom Hook
function useWindowSize() {
  const [size, setSize] = useState({ w: 0, h: 0 });

  useEffect(() => {
    const onResize = () =>
      setSize({ w: window.innerWidth, h: window.innerHeight });
    window.addEventListener('resize', onResize);
    return () => window.removeEventListener('resize', onResize);
  }, []); // Empty = mount only

  return size;
}

// Lazy Init
const [state, setState] = useState(() => computeExpensiveValue());

Reference & Examples

See references/REFERENCE.md.