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The React package contains all the APIs you need to define and work with React components. This page documents all top-level APIs organized by category.

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Components

React provides base classes and utilities for defining components:
  • Component - Base class for React components using ES6 classes
  • PureComponent - Component variant with built-in shallow comparison for props and state

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Creating Elements

These APIs let you create React elements programmatically:

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Refs

Refs provide a way to access DOM nodes or React elements:
  • createRef() - Create a ref object that can be attached to elements via the ref attribute

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Fragments

Fragments let you group multiple elements without adding extra DOM nodes:
  • Fragment or <></> - Group multiple children without a wrapper node

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Context

Context provides a way to pass data through the component tree:
  • createContext(defaultValue) - Create a Context object for sharing data across the component tree

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Higher-Order Components

These APIs wrap components to add additional functionality:
  • forwardRef(render) - Forward refs to child components
  • memo(Component, compare?) - Memoize a component to skip re-renders with same props
  • lazy(load) - Lazy-load a component with dynamic import

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Children Utilities

Utilities for working with the props.children data structure:

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Development Mode Components

These components enable additional checks and features during development:
  • StrictMode - Enable strict mode checks for descendants
  • Profiler - Measure rendering performance of components

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Suspense

Suspense lets you display fallback content while waiting for components to load:
  • Suspense - Display fallback UI while children are loading

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Hooks

Hooks let you use state and other React features in function components:

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State Hooks

  • useState(initialState) - Add state to function components
  • useReducer(reducer, initialArg, init?) - Manage complex state with a reducer

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Effect Hooks

  • useEffect(setup, dependencies?) - Synchronize with external systems
  • useLayoutEffect(setup, dependencies?) - Fires synchronously after all DOM mutations
  • useInsertionEffect(setup, dependencies?) - Fires before any DOM mutations (for CSS-in-JS)

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Ref Hooks

  • useRef(initialValue) - Create a mutable ref object
  • useImperativeHandle(ref, createHandle, dependencies?) - Customize the ref value exposed to parent

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Context Hook

  • useContext(Context) - Read context value

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Performance Hooks

  • useMemo(calculateValue, dependencies) - Cache calculation results
  • useCallback(fn, dependencies) - Cache function definitions

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Transition Hooks

  • useTransition() - Mark state updates as non-urgent transitions
  • useDeferredValue(value, initialValue?) - Defer updating non-urgent parts of UI
  • startTransition(callback) - Mark updates in callback as transitions

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Other Hooks

  • useId() - Generate unique IDs for accessibility attributes
  • useSyncExternalStore(subscribe, getSnapshot, getServerSnapshot?) - Subscribe to external stores
  • use(promise) - Read the value of a Promise or Context
  • useOptimistic(state, updateFn) - Show optimistic state during async operations
  • useActionState(action, initialState, permalink?) - Manage state for form actions
  • useDebugValue(value, format?) - Add a label in React DevTools for custom hooks

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Caching

APIs for caching data and computations:
  • cache(fn) - Cache function results across renders
  • cacheSignal() - Create a signal for cache invalidation

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Unstable APIs

These APIs are experimental and may change:
  • unstable_SuspenseList - Coordinate loading states of multiple Suspense boundaries
  • unstable_LegacyHidden - Hide subtree without unmounting
  • Activity - Track and manage activity states
  • unstable_getCacheForType(resourceType) - Access cache for a specific resource type
  • unstable_useCacheRefresh() - Refresh cached resources
  • unstable_Scope - Create scope for querying DOM elements
  • unstable_TracingMarker - Add markers for performance tracing
  • ViewTransition - Coordinate view transitions
  • unstable_startGestureTransition(callback) - Mark updates as gesture transitions
  • optimisticKey - Special key for optimistic updates

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Development-Only APIs

  • act(callback) - Wrap test code that renders or updates components
  • captureOwnerStack() - Capture the component stack for debugging

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Version

  • version - Current React version string