React hooks reference

Updated 2026-02-15

useState, useEffect, useCallback, useMemo, useRef, and custom hooks. Rules and common patterns.

useState and useEffect

const [state, setState] = useState(initial). setState(prev => prev + 1) for functional update. useEffect(() => { ... }, [deps]); return () => {} for cleanup. Empty [] = mount/unmount only.

useCallback, useMemo, useRef

useCallback(fn, [deps]) memoize function. useMemo(() => value, [deps]) memoize value. useRef(initial) for mutable ref or stable identity; ref.current.

Rules

Only call hooks at top level (no conditionals/loops). Only from React components or custom hooks. Custom hook: function useX() { ... useState ... return ... }.