React is a JavaScript library for building user interfaces.
5 Dec 2024 · Newest first
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UMD builds removed: To load React 19 with a script tag, we recommend using an ESM-based CDN such as esm.sh.
JSX namespace in TypeScript: The global
JSXnamespace is removed to improve interoperability with other libraries using JSX. Instead, the JSX namespace is available from the React package:import { JSX } from 'react'
Removed deprecated TypeScript types:
Deprecated:
element.refaccess: React 19 supports ref as a prop, so we’re deprecatingelement.refin favor ofelement.props.ref. Accessing will result in a warning.
act()no longer checksshouldYieldwhich can be inaccurate in test environments (#26317 by @acdlite)
A transition flowing into a dehydrated boundary no longer suspends when showing fallback (#27230 by @acdlite)
Aborting early no longer infinitely suspends (#24751 by @sebmarkbage)
Below is a list of all new features, APIs, deprecations, and breaking changes. Read React 19 release post and React 19 upgrade guide for more information.
Note: To help make the upgrade to React 19 easier, we’ve published a react@18.3 release that is identical to 18.2 but adds warnings for deprecated APIs and other changes that are needed for React 19. We recommend upgrading to React 18.3.1 first to help identify any issues before upgrading to React 19.
startTransition can now accept async functions. Functions passed to startTransition are called “Actions”. A given Transition can include one or more Actions which update state in the background and update the UI with one commit. In addition to updating state, Actions can now perform side effects including async requests, and the Action will wait for the work to finish before finishing the Transition. This feature allows Transitions to include side effects like fetch() in the pending state, and provides support for error handling, and optimistic updates.useActionState: is a new hook to order Actions inside of a Transition with access to the state of the action, and the pending state. It accepts a reducer that can call Actions, and the initial state used for first render. It also accepts an optional string that is used if the action is passed to a form action prop to support progressive enhancement in forms.useOptimistic: is a new hook to update state while a Transition is in progress. It returns the state, and a set function that can be called inside a transition to “optimistically” update the state to expected final value immediately while the Transition completes in the background. When the transition finishes, the state is updated to the new value.use: is a new API that allows reading resources in render. In React 19, use accepts a promise or Context. If provided a promise, use will suspend until a value is resolved. use can only be used in render but can be called conditionally.ref as a prop: Refs can now be used as props, removing the need for forwardRef.<form> action prop: Form Actions allow you to manage forms automatically and integrate with useFormStatus. When a <form> action succeeds, React will automatically reset the form for uncontrolled components. The form can be reset manually with the new requestFormReset API.<button> and <input> formAction prop: Actions can be passed to the formAction prop to configure form submission behavior. This allows using different Actions depending on the input.useFormStatus: is a new hook that provides the status of the parent <form> action, as if the form was a Context provider. The hook returns the values: pending, data, method, and action.<head> section of the document.<head> on the client before revealing the content of a Suspense boundary that depends on that stylesheet.preinit, preload, prefetchDNS, and preconnect APIs to optimize initial page loads by moving discovery of additional resources like fonts out of stylesheet loading. They can also be used to prefetch resources used by an anticipated navigation.prerender and prerenderToNodeStream APIs for static site generation. They are designed to work with streaming environments like Node.js Streams and Web Streams. Unlike renderToString, they wait for data to load for HTML generation.element.ref access: React 19 supports ref as a prop, so we’re deprecating element.ref in favor of element.props.ref. Accessing will result in a warning.react-test-renderer: In React 19, react-test-renderer logs a deprecation warning and has switched to concurrent rendering for web usage. We recommend migrating your tests to @testinglibrary.com/docs/react-testing-library/intro/) or @testingesting-library.com/docs/react-native-testing-library/intro)React 19 brings in a number of breaking changes, including the removals of long-deprecated APIs. We recommend first upgrading to 18.3.1, where we've added additional deprecation warnings. Check out the upgrade guide for more details and guidance on codemodding.
onUncaughtError and onCaughtError methods to createRoot and hydrateRoot to customize this error handling.propTypes: Using propTypes will now be silently ignored. If required, we recommend migrating to TypeScript or another type-checking solution.defaultProps for functions: ES6 default parameters can be used in place. Class components continue to support defaultProps since there is no ES6 alternative.contextTypes and getChildContext: Legacy Context for class components has been removed in favor of the contextType API.React.createFactory: Now that JSX is broadly supported, all createFactory usage can be migrated to JSX components.react-test-renderer/shallow: This has been a re-export of react-shallow-renderer since React 18. If needed, you can continue to use the third-party package directly. We recommend using @testinglibrary.com/docs/react-testing-library/intro/) or @testingesting-library.com/docs/react-native-testing-library/intro) instead.react-dom/test-utils: We’ve moved from to react. All other utilities have been removed.<Context> as a provider: You can now render <Context> as a provider instead of <Context.Provider>.useDeferredValue initial value argument: When provided, useDeferredValue will return the initial value for the initial render of a component, then schedule a re-render in the background with the deferredValue returned.useMemo and useCallback will now reuse the memoized results from the first render, during the second render. Additionally, StrictMode will now double-invoke ref callback functions on initial mount.The most common changes can be codemodded with npx types-react-codemod@latest preset-19 ./path-to-your-react-ts-files.
ReactChild (replacement: React.ReactElement | number | string)ReactFragment (replacement: Iterable<React.ReactNode>)ReactNodeArray (replacement: ReadonlyArray<React.ReactNode>)ReactText (replacement: number | string)VoidFunctionComponent (replacement: FunctionComponent)VFC (replacement: FC)prop-types: Requireable, ValidationMap, Validator, WeakValidationMapcreate-react-class: ClassicComponentClass, ClassicComponent, ClassicElement, ComponentSpec, Mixin, ReactChildren, ReactHTML, ReactSVG, SFCFactoryuseRef: The initial argument is now required to match useState, createContext etcuseRef() are now always mutable instead of sometimes being immutable. This feature was too confusing for users and conflicted with legit cases where refs were managed by React and manually written to.ReactElement typing: The props of React elements now default to unknown instead of any if the element is typed as ReactElementJSX namespace is removed to improve interoperability with other libraries using JSX. Instead, the JSX namespace is available from the React package: import { JSX } from 'react'useReducer typings: Most useReducer usage should not require explicit type arguments.-useReducer<React.Reducer<State, Action>>(reducer)
+useReducer(reducer)
-useReducer<React.Reducer<State, Action>>(reducer)
+useReducer<State, [Action]>(reducer)
useActionState() hook to update state based on the result of a Form Action (#27270, #27278, #27309, #27302, #27307, #27366, #27370, #27321, #27374, #27372, #27397, #27399, #27460, #28557, #27570, #27571, #28631, #28788, #29694, #29695, , , , by @acdlite, @eps1lon, and @rickhanlonii)useFormStatus() hook to provide status information of the last form submission (#26719, #26722, #26788, #29019, #28728, #28413 by @acdlite and @eps1lon)preinit, preinitModule, preconnect, prefetchDNS, preload, and preloadModule APIs.
bootstrapScripts and bootstrapModules (#25104 by @gnoff)bootstrapModules, bootstrapScripts, and update priority queue (#26754, #26753, #27190, #27189 by @gnoff)react-test-renderer on web (#27903, #28904 by @jackpope and @acdlite)react-test-renderer/shallow export (#25475, #28497 by @sebmarkbage and @jackpope)prepareUpdate (#26583, #27409 by @sebmarkbage and @sophiebits)isConcurrentMode and isAsyncMode methods (#28224 by @gaearon)actreact-dom/test-utilsReactDOM.render, ReactDOM.hydrate: These have been removed in favor of the concurrent equivalents: ReactDOM.createRoot and ReactDOM.hydrateRoot.unmountComponentAtNode: Removed in favor of root.unmount().ReactDOM.findDOMNode: You can replace ReactDOM.findDOMNode with DOM Refs.use() API to read resources in render (#25084, #25202, #25207, #25214, #25226, #25247, #25539, #25538, #25537, #25543, #25561, #25620, #25615, #25922, #25641, #25634, #26232, #26536, #26739, #28233 by @acdlite, @MofeiZ, @sebmarkbage, @sophiebits, @eps1lon, and @hansottowirtz)useOptimistic() hook to display mutated state optimistically during an async mutation (#26740, #26772, #27277, #27453, #27454, #27936 by @acdlite)initialValue argument to useDeferredValue() hook (#27500, #27509, #27512, #27888, #27550 by @acdlite)<Context> to mean <Context.Provider> (#28226 by @gaearon)info, group, and groupCollapsed in StrictMode logging (#25172 by @timneutkens)useSyncExternalStore() hydration in StrictMode (#26791 by @sophiebits)componentWillUnmount() in StrictMode (#26842 by @tyao1)useState() and useReducer() initializer functions in StrictMode (#28248 by @eps1lon)useId() in StrictMode (#25713 by @gnoff)act() no longer checks shouldYield which can be inaccurate in test environments (#26317 by @acdlite)react.element symbol to react.transitional.element (#28813 by @sebmarkbage)useSyncExternalStore() re-render (#27199 by @acdlite)useSyncExternalStore() dropped update when state is dispatched in render phase (#25578 by @pandaiolo)RefreshRuntime.findAffectedHostInstances (#30538 by @gaearon)defaultProps support, except for classes (#28733 by @acdlite)createFactory (#27798 by @kassens)fetchPriority to <img> and <link> (#25927 by @styfle)transformOrigin prop (#26130 by @aravarav-ind))onScrollEnd event (#26789 by @devongovett)<hr> as child of <select> (#27632 by @SouSingh)inert (#24730 by @eps1lon)imageSizes and imageSrcSet (#22550 by @eps1lon)flushSync exhausts queue even if something throws (#26366 by @acdlite)react and react-dom versions don’t match (#29236 by @acdlite)srcset and src are assigned last on <img> instances (#30340 by @gnoff)src and href attributes (unless for <a href=”” />) (#18513, #28124 by @bvaughn and @eps1lon)scale style property (#25601 by @JonnyBurger)onChange error message for controlled <select> (#27740 by @BikiBiki-das))render, hydrate, findDOMNode, unmountComponentAtNode, unstable_createEventHandle, unstable_renderSubtreeIntoContainer, and unstable_runWithPriority. Move createRoot and hydrateRoot to react-dom/client. (#28271 by @gnoff)test-utils (#28541 by @eps1lon)unstable_flushControlled (#26397 by @kassens)renderToStaticNodeStream() (#28873 by @gnoff)unstable_renderSubtreeIntoContainer (#29771 by @kassens)<style> and <script> textContent to enable rendering inner content without dangerouslySetInnerHTML (#28870, #28871 by @gnoff)srcset to trigger load event on mount (#30351 by @gnoff)onError (#27761, #27850 by @gnoff and @sebmarkbage)crossorigin support to bootstrap scripts (#26844 by @HenriqueLimas)nonce and fetchpriority in preload links (#26826 by @liuyenwei)referrerPolicy to ReactDOM.preload() (#27096 by @styfle)react/jsx-dev-runtime (#28921 by @himself65)errorInfo.digest from onRecoverableError (#28222 by @gnoff)