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React
v19.1
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    react@19.1

  • Overview
  • Hooks
    • useActionState
    • useCallback
    • useContext
    • useDebugValue
    • useDeferredValue
    • useEffect
    • useId
    • useImperativeHandle
    • useInsertionEffect
    • useLayoutEffect
    • useMemo
    • useOptimistic
    • useReducer
    • useRef
    • useState
    • useSyncExternalStore
    • useTransition
  • Components
    • <Fragment> (<>)
    • <Profiler>
    • <StrictMode>
    • <Suspense>
    • <Activity> - This feature is available in the latest Canary version of React
    • <ViewTransition> - This feature is available in the latest Experimental version of React
  • APIs
    • act
    • cache
    • captureOwnerStack
    • createContext
    • lazy
    • memo
    • startTransition
    • use
    • experimental_taintObjectReference - This feature is available in the latest Experimental version of React
    • experimental_taintUniqueValue - This feature is available in the latest Experimental version of React
    • unstable_addTransitionType - This feature is available in the latest Experimental version of React

  • react-dom@19.1

  • Hooks
    • useFormStatus
  • Components
    • Common (e.g. <div>)
    • <form>
    • <input>
    • <option>
    • <progress>
    • <select>
    • <textarea>
    • <link>
    • <meta>
    • <script>
    • <style>
    • <title>
  • APIs
    • createPortal
    • flushSync
    • preconnect
    • prefetchDNS
    • preinit
    • preinitModule
    • preload
    • preloadModule
  • Client APIs
    • createRoot
    • hydrateRoot
  • Server APIs
    • renderToPipeableStream
    • renderToReadableStream
    • renderToStaticMarkup
    • renderToString
  • Static APIs
    • prerender
    • prerenderToNodeStream

  • React Compiler

  • Configuration
    • compilationMode
    • gating
    • logger
    • panicThreshold
    • target
  • Directives
    • "use memo"
    • "use no memo"
  • Compiling Libraries

  • Rules of React

  • Overview
    • Components and Hooks must be pure
    • React calls Components and Hooks
    • Rules of Hooks

  • React Server Components

  • Server Components
  • Server Functions
  • Directives
    • 'use client'
    • 'use server'

  • Legacy APIs

  • Legacy React APIs
    • Children
    • cloneElement
    • Component
    • createElement
    • createRef
    • forwardRef
    • isValidElement
    • PureComponent

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On this page

  • Overview
  • Reference
  • useEffect(setup, dependencies?)
  • Usage
  • Connecting to an external system
  • Wrapping Effects in custom Hooks
  • Controlling a non-React widget
  • Fetching data with Effects
  • Specifying reactive dependencies
  • Updating state based on previous state from an Effect
  • Removing unnecessary object dependencies
  • Removing unnecessary function dependencies
  • Reading the latest props and state from an Effect
  • Displaying different content on the server and the client
  • Troubleshooting
  • My Effect runs twice when the component mounts
  • My Effect runs after every re-render
  • My Effect keeps re-running in an infinite cycle
  • My cleanup logic runs even though my component didn’t unmount
  • My Effect does something visual, and I see a flicker before it runs