React Hooks are functions that let you use state and lifecycle features in functional components.
Introduced in React 16.8 to replace class components.

useState: manages local component state.
Syntax: const [state, setState] = useState(initialValue)
Example: const [count, setCount] = useState(0)

useEffect: handles side effects like API calls, subscriptions, DOM updates.
Runs after every render by default.
Syntax: useEffect(() => { /* effect */ }, [dependencies])
Empty dependency array [] means run only once on mount.

useContext: consume React context without wrapping in Consumer component.
Syntax: const value = useContext(MyContext)

useRef: holds mutable value that does not trigger re-render. Also used to access DOM elements.

Rules of Hooks:
1. Only call hooks at the top level (not inside loops or conditions).
2. Only call hooks from React function components or custom hooks.