Hooks API

React · Methods reference

React · Methods reference

📋 Overview

All built-in React hooks (React 19) — rules: only call at top level in function components or custom hooks.

🔧 Methods

State & refs

Hook	Description
`useState(initial)`	Returns [state, setState]
`useReducer(reducer, init)`	State via reducer dispatch
`useRef(initial)`	Mutable ref object (.current)
`useImperativeHandle(ref, create, deps?)`	Customize ref exposed to parent

Effects & lifecycle

Hook	Description
`useEffect(fn, deps?)`	After paint side effects; cleanup return
`useLayoutEffect(fn, deps?)`	After DOM mutations, before paint
`useInsertionEffect(fn, deps?)`	Before layout effects (CSS-in-JS libs)

Context & memoization

Hook	Description
`useContext(Ctx)`	Read nearest context value
`useMemo(fn, deps)`	Memoize expensive computed value
`useCallback(fn, deps)`	Memoize function reference

Concurrent & IDs

Hook	Description
`useTransition()`	[isPending, startTransition] — non-urgent updates
`useDeferredValue(value)`	Defer re-render of heavy UI
`useId()`	Stable unique IDs for a11y
`useSyncExternalStore(sub, getSnap, getServerSnap?)`	Subscribe external store
`useActionState(action, initialState)`	Form action state (19)
`useOptimistic(state, updateFn)`	Optimistic UI (19)
`useFormStatus()`	Pending state from parent form (19)

💡 Examples

See parent topic notes for runnable snippets; this page is the complete method index.

⚠️ Pitfalls

Mutating methods return None in Python — do not chain sort() / reverse() expecting a new list.
Default JS sort() compares strings — pass (a,b) => a-b for numbers.
SQL function names differ by dialect — verify Postgres vs MySQL docs.
Django QuerySet.update() skips save() signals and auto auto_now fields on models.

Component API

React · Methods reference

React DOM Methods

React · Methods reference

On this page

📋 Overview 🔧 Methods State & refs Effects & lifecycle Context & memoization Concurrent & IDs 💡 Examples ⚠️ Pitfalls 🔗 Related