React Hooks Deep Dive for Senior Frontend Interviews
useState batching, useEffect cleanup, useMemo vs useCallback, custom hooks, and rules of hooks — with patterns interviewers expect at senior level. useEffect: dependencies and cleanup. React 18+ changed batching behavior and concurrent features. Senior interviews now test whether you understand when hooks re-run, how to avoid stale closures, and when memoization helps vs hurts. useMemo vs useCallback. Every effect that subscribes, timers, or fetches must return a cleanup function. Missing cleanup causes memory leaks and race conditions. Custom hooks interviewers ask you to build.