Stale closures in useEffect or timers — state stuck at initial value

Inside a useEffect, I use state variables or functions that seem “frozen” even after updates. For example, a counter set by interval never increments past the initial value.

JavaScript closures capture initial values at render time, so callbacks inside useEffect don’t see later updates. This stale state causes incorrect behavior ([turn0reddit23], [turn0reddit17]). Fixes: • Use functional updates: setCount(prev => prev + 1) • Move definitions inside the effect, or use refs to store current values. • Ensure dependencies include the functions or state used, memoized via useCallback where necessary.