Today, we are releasing React 17!

Learn more about React 17 and how to update to it on the official React blog.

React

• Add react/jsx-runtime and react/jsx-dev-runtime for the new JSX transform. (@lunaruan in #18299)
• Build component stacks from native error frames. (@sebmarkbage in #18561)
• Allow to specify displayName on context for improved stacks. (@eps1lon in #18224)
• Prevent 'use strict' from leaking in the UMD bundles. (@koba04 in #19614)
• Stop using fb.me for redirects. (@cylim in #19598)

React DOM

• Delegate events to roots instead of document. (@trueadm in #18195 and others)
• Clean up all effects before running any next effects. (@bvaughn in #17947)
• Run useEffect cleanup functions asynchronously. (@bvaughn in #17925)
• Use browser focusin and focusout for onFocus and onBlur. (@trueadm in #19186)
• Make all Capture events use the browser capture phase. (@trueadm in #19221)
• Don't emulate bubbling of the onScroll event. (@gaearon in #19464)
• Throw if forwardRef or memo component returns undefined. (@gaearon in #19550)
• Remove event pooling. (@trueadm in #18969)
• Stop exposing internals that won’t be needed by React Native Web. (@necolas in #18483)
• Attach all known event listeners when the root mounts. (@gaearon in #19659)
• Disable console in the second render pass of DEV mode double render. (@sebmarkbage in #18547)
• Deprecate the undocumented and misleading ReactTestUtils.SimulateNative API. (@gaearon in #13407)
• Rename private field names used in the internals. (@gaearon in #18377)
• Don't call User Timing API in development. (@gaearon in #18417)
• Disable console during the repeated render in Strict Mode. (@sebmarkbage in #18547)
• In Strict Mode, double-render components without Hooks too. (@eps1lon in #18430)
• Allow calling ReactDOM.flushSync during lifecycle methods (but warn). (@sebmarkbage in #18759)
• Add the code property to the keyboard event objects. (@bl00mber in #18287)
• Add the disableRemotePlayback property for video elements. (@tombrowndev in #18619)
• Add the enterKeyHint property for input elements. (@eps1lon in #18634)
• Warn when no value is provided to <Context.Provider>. (@charlie1404 in #19054)
• Warn when memo or forwardRef components return undefined. (@bvaughn in #19550)
• Improve the error message for invalid updates. (@JoviDeCroock in #18316)
• Exclude forwardRef and memo from stack frames. (@sebmarkbage in #18559)
• Improve the error message when switching between controlled and uncontrolled inputs. (@vcarl in #17070)
• Keep onTouchStart, onTouchMove, and onWheel passive. (@gaearon in #19654)
• Fix setState hanging in development inside a closed iframe. (@gaearon in #19220)
• Fix rendering bailout for lazy components with defaultProps. (@jddxf in #18539)
• Fix a false positive warning when dangerouslySetInnerHTML is undefined. (@eps1lon in #18676)
• Fix Test Utils with non-standard require implementation. (@just-boris in #18632)
• Fix onBeforeInput reporting an incorrect event.type. (@eps1lon in #19561)
• Fix event.relatedTarget reported as undefined in Firefox. (@claytercek in #19607)
• Fix "unspecified error" in IE11. (@hemakshis in #19664)
• Fix rendering into a shadow root. (@Jack-Works in #15894)
• Fix movementX/Y polyfill with capture events. (@gaearon in #19672)
• Use delegation for onSubmit and onReset events. (@gaearon in #19333)
• Improve memory usage. (@trueadm in #18970)

React DOM Server

• Make useCallback behavior consistent with useMemo for the server renderer. (@alexmckenley in #18783)
• Fix state leaking when a function component throws. (@pmaccart in #19212)

React Test Renderer

• Improve findByType error message. (@henryqdineen in #17439)

Concurrent Mode (Experimental)

• Revamp the priority batching heuristics. (@acdlite in #18796)
• Add the unstable_ prefix before the experimental APIs. (@acdlite in #18825)
• Remove unstable_discreteUpdates and unstable_flushDiscreteUpdates. (@trueadm in #18825)
• Remove the timeoutMs argument. (@acdlite in #19703)
• Disable <div hidden /> prerendering in favor of a different future API. (@acdlite in #18917)
• Add unstable_expectedLoadTime to Suspense for CPU-bound trees. (@acdlite in #19936)
• Add an experimental unstable_useOpaqueIdentifier Hook. (@lunaruan in #17322)
• Add an experimental unstable_startTransition API. (@rickhanlonii in #19696)
• Using act in the test renderer no longer flushes Suspense fallbacks. (@acdlite in #18596)
• Use global render timeout for CPU Suspense. (@sebmarkbage in #19643)
• Clear the existing root content before mounting. (@bvaughn in #18730)
• Fix a bug with error boundaries. (@acdlite in #18265)
• Fix a bug causing dropped updates in a suspended tree. (@acdlite in #18384 and #18457)
• Fix a bug causing dropped render phase updates. (@acdlite in #18537)
• Fix a bug in SuspenseList. (@sebmarkbage in #18412)
• Fix a bug causing Suspense fallback to show too early. (@acdlite in #18411)
• Fix a bug with class components inside SuspenseList. (@sebmarkbage in #18448)
• Fix a bug with inputs that may cause updates to be dropped. (@jddxf in #18515 and @acdlite in #18535)
• Fix a bug causing Suspense fallback to get stuck. (@acdlite in #18663)
• Don't cut off the tail of a SuspenseList if hydrating. (@sebmarkbage in #18854)
• Fix a bug in useMutableSource that may happen when getSnapshot changes. (@bvaughn in #18297)
• Fix a tearing bug in useMutableSource. (@bvaughn in #18912)
• Warn if calling setState outside of render but before commit. (@sebmarkbage in #18838)

Artifacts

• react: https://unpkg.com/react@17.0.1/umd/
• react-art: https://unpkg.com/react-art@17.0.1/umd/
• react-dom: https://unpkg.com/react-dom@17.0.1/umd/
• react-is: https://unpkg.com/react-is@17.0.1/umd/
• react-test-renderer: https://unpkg.com/react-test-renderer@17.0.1/umd/
• scheduler: https://unpkg.com/scheduler@0.20.1/umd/

React

• Add support for the new JSX transform. (@lunaruan in #18299)

React DOM

• Fix bug in legacy mode Suspense where effect clean-up functions are not fired. This only affects users who use Suspense for data fetching in legacy mode, which is not technically supported. (@acdlite in #18238)
• Revert warning for cross-component updates that happen inside class render lifecycles (componentWillReceiveProps, shouldComponentUpdate, and so on). (@gaearon in #18330)

Artifacts

• react: https://unpkg.com/react@16.13.1/umd/
• react-art: https://unpkg.com/react-art@16.13.1/umd/
• react-dom: https://unpkg.com/react-dom@16.13.1/umd/
• react-is: https://unpkg.com/react-is@16.13.1/umd/
• react-test-renderer: https://unpkg.com/react-test-renderer@16.13.1/umd/
• scheduler: https://unpkg.com/scheduler@0.19.1/umd/

React DOM

• Fix passive effects (useEffect) not being fired in a multi-root app. (@acdlite in #17347)

React Is

• Fix lazy and memo types considered elements instead of components (@bvaughn in #17278)

Artifacts

• react: https://unpkg.com/react@16.12.0/umd/
• react-art: https://unpkg.com/react-art@16.12.0/umd/
• react-dom: https://unpkg.com/react-dom@16.12.0/umd/
• react-is: https://unpkg.com/react-is@16.12.0/umd/
• react-test-renderer: https://unpkg.com/react-test-renderer@16.12.0/umd/
• scheduler: https://unpkg.com/scheduler@0.18.0/umd/

React DOM

• Fix mouseenter handlers from firing twice inside nested React containers. @yuanoook in #16928
• Remove unstable_createRoot and unstable_createSyncRoot experimental APIs. (These are available in the Experimental channel as createRoot and createSyncRoot.) (@acdlite in #17088)

Artifacts

• react: https://unpkg.com/react@16.11.0/umd/
• react-art: https://unpkg.com/react-art@16.11.0/umd/
• react-dom: https://unpkg.com/react-dom@16.11.0/umd/
• react-is: https://unpkg.com/react-is@16.11.0/umd/
• react-test-renderer: https://unpkg.com/react-test-renderer@16.11.0/umd/
• scheduler: https://unpkg.com/scheduler@0.17.0/umd/

React DOM

• Fix regression in react-native-web by restoring order of arguments in event plugin extractors (@necolas in #16978)

Artifacts

• react: https://unpkg.com/react@16.10.2/umd/
• react-art: https://unpkg.com/react-art@16.10.2/umd/
• react-dom: https://unpkg.com/react-dom@16.10.2/umd/
• react-is: https://unpkg.com/react-is@16.10.2/umd/
• react-test-renderer: https://unpkg.com/react-test-renderer@16.10.2/umd/
• scheduler: https://unpkg.com/scheduler@0.16.2/umd/

React DOM

• Fix regression in Next.js apps by allowing Suspense mismatch during hydration to silently proceed (@sebmarkbage in #16943)

React

• Add <React.Profiler> API for gathering performance measurements programmatically. (@bvaughn in #15172)
• Remove unstable_ConcurrentMode in favor of unstable_createRoot. (@acdlite in #15532)

React DOM

• Deprecate old names for the UNSAFE_* lifecycle methods. (@bvaughn in #15186 and @threepointone in #16103)
• Deprecate javascript: URLs as a common attack surface. (@sebmarkbage in #15047)
• Deprecate uncommon "module pattern" (factory) components. (@sebmarkbage in #15145)
• Add support for the disablePictureInPicture attribute on <video>. (@eek in #15334)
• Add support for onLoad event for <embed>. (@cherniavskii in #15614)
• Add support for editing useState state from DevTools. (@bvaughn in #14906)
• Add support for toggling Suspense from DevTools. (@gaearon in #15232)
• Warn when setState is called from useEffect, creating a loop. (@gaearon in #15180)
• Fix a memory leak. (@paulshen in #16115)
• Fix a crash inside findDOMNode for components wrapped in <Suspense>. (@acdlite in #15312)
• Fix pending effects from being flushed too late. (@acdlite in #15650)
• Fix incorrect argument order in a warning message. (@brickspert in #15345)
• Fix hiding Suspense fallback nodes when there is an !important style. (@acdlite in #15861 and #15882)
• Slightly improve hydration performance. (@bmeurer in #15998)

React DOM Server

• Fix incorrect output for camelCase custom CSS property names. (@bedakb in #16167)

React Test Utilities and Test Renderer

• Add act(async () => ...) for testing asynchronous state updates. (@threepointone in #14853)
• Add support for nesting act from different renderers. (@threepointone in #16039 and #16042)
• Warn in Strict Mode if effects are scheduled outside an act() call. (@threepointone in #15763 and #16041)
• Warn when using act from the wrong renderer. (@threepointone in #15756)

Artifacts

• react: https://unpkg.com/react@16.9.0/umd/
• react-art: https://unpkg.com/react-art@16.9.0/umd/
• react-dom: https://unpkg.com/react-dom@16.9.0/umd/
• react-is: https://unpkg.com/react-is@16.9.0/umd/
• react-test-renderer: https://unpkg.com/react-test-renderer@16.9.0/umd/
• scheduler: https://unpkg.com/scheduler@0.15.0/umd/

This is a release candidate for React v16.9.0.

Changelog is available in #16254.

UMD builds

• react: https://unpkg.com/react@16.9.0-rc.0/umd/
• react-art: https://unpkg.com/react-art@16.9.0-rc.0/umd/
• react-dom: https://unpkg.com/react-dom@16.9.0-rc.0/umd/
• react-is: https://unpkg.com/react-is@16.9.0-rc.0/umd/
• react-test-renderer: https://unpkg.com/react-test-renderer@16.9.0-rc.0/umd/
• scheduler: https://unpkg.com/scheduler@0.15.0-rc.0/umd/

v16.9.0-alpha.0 (April 3, 2019)

• (await act(async () => ...) (@threepointone in #14853)

Artifacts

• react: https://unpkg.com/react@16.9.0-alpha.0/umd/
• react-art: https://unpkg.com/react-art@16.9.0-alpha.0/umd/
• react-dom: https://unpkg.com/react-dom@16.9.0-alpha.0/umd/
• react-is: https://unpkg.com/react-is@16.9.0-alpha.0/umd/
• react-test-renderer: https://unpkg.com/react-test-renderer@16.9.0-alpha.0/umd/
• scheduler: https://unpkg.com/scheduler@0.14.0-alpha.0/umd/

16.8.6 (March 27, 2019)

React DOM

• Fix an incorrect bailout in useReducer(). (@acdlite in #15124)
• Fix iframe warnings in Safari DevTools. (@renanvalentin in #15099)
• Warn if contextType is set to Context.Consumer instead of Context. (@aweary in #14831)
• Warn if contextType is set to invalid values. (@gaearon in #15142)

Artifacts

• react: https://unpkg.com/react@16.8.6/umd/
• react-art: https://unpkg.com/react-art@16.8.6/umd/
• react-dom: https://unpkg.com/react-dom@16.8.6/umd/
• react-is: https://unpkg.com/react-is@16.8.6/umd/
• react-test-renderer: https://unpkg.com/react-test-renderer@16.8.6/umd/
• scheduler: https://unpkg.com/scheduler@0.13.6/umd/

16.8.4 (March 5, 2019)

React DOM and other renderers

• Fix a bug where DevTools caused a runtime error when inspecting a component that used a useContext hook. (@bvaughn in #14940)

16.8.2 (February 14, 2019)

React DOM

• Fix ReactDOM.render being ignored inside useEffect. (@gaearon in #14799)
• Fix a crash when unmounting empty portals. (@gaearon in #14820)
• Fix useImperativeHandle to work correctly when no deps are specified. (@gaearon in #14801)
• Fix crossOrigin attribute to work in SVG image elements. (@aweary in #14832)
• Fix a false positive warning when using Suspense with Hooks. (@gaearon in #14821)

React Test Utils and React Test Renderer

• Include component stack into the act() warning. (@threepointone in #14855)

Artifacts

• react: https://unpkg.com/react@16.8.2/umd/
• react-art: https://unpkg.com/react-art@16.8.2/umd/
• react-dom: https://unpkg.com/react-dom@16.8.2/umd/
• react-is: https://unpkg.com/react-is@16.8.2/umd/
• react-test-renderer: https://unpkg.com/react-test-renderer@16.8.2/umd/
• scheduler: https://unpkg.com/scheduler@0.13.2/umd/

16.8.1 (February 6, 2019)

React DOM and React Test Renderer

• Fix a crash when used together with an older version of React. (@bvaughn in #14770)

React Test Utils

• Fix a crash in Node environment. (@threepointone in #14768)

React DOM

• Fix performance of React.lazy for large numbers of lazily-loaded components. (@acdlite in #14429)
• Clear fields on unmount to avoid memory leaks. (@trueadm in #14276)
• Fix bug with SSR and context when mixing react-dom/server@16.6 and react@<16.6. (@gaearon in #14291)
• Fix a performance regression in profiling mode. (@bvaughn in #14383)

Scheduler (Experimental)

• Post to MessageChannel instead of window. (@acdlite in #14234)
• Reduce serialization overhead. (@developit in #14249)
• Fix fallback to setTimeout in testing environments. (@bvaughn in #14358)
• Add methods for debugging. (@mrkev in #14053)

16.6.3 (November 12, 2018)

React DOM

• Fix bugs in Suspense and lazy. (@acdlite in #14133, #14157, and #14164)
• Fix highlighting of React.memo updates in React DevTools. (@bvaughn in #14141)
• Fix interaction of Suspense with the React Profiler. (@bvaughn in #14065)
• Fix a false positive warning when using Suspense. (@acdlite in #14158)

React DOM Server

• Fix incorrect sharing of context state between renderToNodeStream() calls. (@sebmarkbage in #14182)
• Add a warning about incorrect usage of the context API. (@trueadm in #14033)

16.6.1 (November 6, 2018)

React DOM

• Fallback should not remount every time a promise resolves. (@acdlite in #14083)
• Fix bug where Suspense keeps showing fallback even after everything finishes loading. (@acdlite in #14083)
• Fix unresolved default props in lifecycle methods of a lazy component. (@gaearon in #14112)
• Fix bug when recovering from an error thrown during complete phase. (@gaearon in #14104)

Scheduler (Experimental)

• Switch from deadline object to shouldYield API. (@acdlite in #14025)

16.6.0 (October 23, 2018)

React

• Add React.memo() as an alternative to PureComponent for functions. (@acdlite in #13748)
• Add React.lazy() for code splitting components. (@acdlite in #13885)
• React.StrictMode now warns about legacy context API. (@bvaughn in #13760)
• React.StrictMode now warns about findDOMNode. (@sebmarkbage in #13841)
• Rename unstable_AsyncMode to unstable_ConcurrentMode. (@trueadm in #13732)
• Rename unstable_Placeholder to Suspense, and delayMs to maxDuration. (@gaearon in #13799 and @sebmarkbage in #13922)

React DOM

• Add contextType as a more ergonomic way to subscribe to context from a class. (@bvaughn in #13728)
• Add getDerivedStateFromError lifecycle method for catching errors in a future asynchronous server-side renderer. (@bvaughn in #13746)
• Warn when <Context> is used instead of <Context.Consumer>. (@trueadm in #13829)
• Fix gray overlay on iOS Safari. (@philipp-spiess in #13778)
• Fix a bug caused by overwriting window.event in development. (@sergei-startsev in #13697)

React DOM Server

• Add support for React.memo(). (@alexmckenley in #13855)
• Add support for contextType. (@alexmckenley and @sebmarkbage in #13889)

Scheduler (Experimental)

• Rename the package to scheduler. (@gaearon in #13683)
• Support priority levels, continuations, and wrapped callbacks. (@acdlite in #13720 and #13842)
• Improve the fallback mechanism in non-DOM environments. (@acdlite in #13740)
• Schedule requestAnimationFrame earlier. (@acdlite in #13785)
• Fix the DOM detection to be more thorough. (@trueadm in #13731)
• Fix bugs with interaction tracing. (@bvaughn in #13590)
• Add the envify transform to the package. (@mridgway in #13766)

16.4.2 (August 1, 2018)

React DOM Server

• Fix a potential XSS vulnerability when the attacker controls an attribute name (CVE-2018-6341). This fix is available in the latest react-dom@16.4.2, as well as in previous affected minor versions: react-dom@16.0.1, react-dom@16.1.2, react-dom@16.2.1, and react-dom@16.3.3. (@gaearon in #13302)

• Fix a crash in the server renderer when an attribute is called hasOwnProperty. This fix is only available in react-dom@16.4.2. (@gaearon in #13303)

16.4.1 (June 13, 2018)

React

• You can now assign propTypes to components returned by React.ForwardRef. (@bvaughn in #12911)

React DOM

• Fix a crash when the input type changes from some other types to text. (@spirosikmd in #12135)
• Fix a crash in IE11 when restoring focus to an SVG element. (@ThaddeusJiang in #12996)
• Fix a range input not updating in some cases. (@Illu in #12939)
• Fix input validation triggering unnecessarily in Firefox. (@nhunzaker in #12925)
• Fix an incorrect event.target value for the onChange event in IE9. (@nhunzaker in #12976)
• Fix a false positive error when returning an empty <React.Fragment /> from a component. (@philipp-spiess in #12966)

React DOM Server

• Fix an incorrect value being provided by new context API. (@ericsoderberghp in #12985, @gaearon in #13019)

React Test Renderer

• Allow multiple root children in test renderer traversal API. (@gaearon in #13017)
• Fix getDerivedStateFromProps() in the shallow renderer to not discard the pending state. (@fatfisz in #13030)

React

• Add a new experimental React.unstable_Profiler component for measuring performance. (@bvaughn in #12745)

React DOM

• Add support for the Pointer Events specification. (@philipp-spiess in #12507)
• Properly call getDerivedStateFromProps() regardless of the reason for re-rendering. (@acdlite in #12600 and #12802)
• Fix a bug that prevented context propagation in some cases. (@gaearon in #12708)
• Fix re-rendering of components using forwardRef() on a deeper setState(). (@gaearon in #12690)
• Fix some attributes incorrectly getting removed from custom element nodes. (@airamrguez in #12702)
• Fix context providers to not bail out on children if there's a legacy context provider above. (@gaearon in #12586)
• Add the ability to specify propTypes on a context provider component. (@nicolevy in #12658)
• Fix a false positive warning when using react-lifecycles-compat in <StrictMode>. (@bvaughn in #12644)
• Warn when the forwardRef() render function has propTypes or defaultProps. (@bvaughn in #12644)
• Improve how forwardRef() and context consumers are displayed in the component stack. (@sophiebits in #12777)
• Change internal event names. This can break third-party packages that rely on React internals in unsupported ways. (@philipp-spiess in #12629)

React Test Renderer

• Fix the getDerivedStateFromProps() support to match the new React DOM behavior. (@koba04 in #12676)
• Fix a testInstance.parent crash when the parent is a fragment or another special node. (@gaearon in #12813)
• forwardRef() components are now discoverable by the test renderer traversal methods. (@gaearon in #12725)
• Shallow renderer now ignores setState() updaters that return null or undefined. (@koba04 in #12756)

React ART

• Fix reading context provided from the tree managed by React DOM. (@acdlite in #12779)

React Call Return (Experimental)

• This experiment was deleted because it was affecting the bundle size and the API wasn't good enough. It's likely to come back in the future in some other form. (@gaearon in #12820)

React Reconciler (Experimental)

• The new host config shape is flat and doesn't use nested objects. (@gaearon in #12792)

16.3.2 (April 16, 2018)

React

• Improve the error message when passing null or undefined to React.cloneElement. (@nicolevy in #12534)

React DOM

• Fix an IE crash in development when using <StrictMode>. (@bvaughn in #12546)
• Fix labels in User Timing measurements for new component types. (@bvaughn in #12609)
• Improve the warning about wrong component type casing. (@nicolevy in #12533)
• Improve general performance in development mode. (@gaearon in #12537)
• Improve performance of the experimental unstable_observedBits API with nesting. (@gaearon in #12543)

React Test Renderer

• Add a UMD build. (@bvaughn in #12594)

16.3.1 (April 3, 2018)

React

• Fix a false positive warning in IE11 when using Fragment. (@heikkilamarko in #12504)
• Prefix a private API. (@Andarist in #12501)
• Improve the warning when calling setState() in constructor. (@gaearon in #12532)

React DOM

• Fix getDerivedStateFromProps() not getting applied in some cases. (@acdlite in #12528)
• Fix a performance regression in development mode. (@gaearon in #12510)
• Fix error handling bugs in development mode. (@gaearon and @acdlite in #12508)
• Improve user timing API messages for profiling. (@flarnie in #12384)

Create Subscription

• Set the package version to be in sync with React releases. (@bvaughn in #12526)
• Add a peer dependency on React 16.3+. (@NMinhNguyen in #12496)

16.3.0 (March 29, 2018)

React

• Add a new officially supported context API. (@acdlite in #11818)
• Add a new React.createRef() API as an ergonomic alternative to callback refs. (@trueadm in #12162)
• Add a new React.forwardRef() API to let components forward their refs to a child. (@bvaughn in #12346)
• Fix a false positive warning in IE11 when using React.Fragment. (@XaveScor in #11823)
• Replace React.unstable_AsyncComponent with React.unstable_AsyncMode. (@acdlite in #12117)
• Improve the error message when calling setState() on an unmounted component. (@sophiebits in #12347)

React DOM

• Add a new getDerivedStateFromProps() lifecycle and UNSAFE_ aliases for the legacy lifecycles. (@bvaughn in #12028)
• Add a new getSnapshotBeforeUpdate() lifecycle. (@bvaughn in #12404)
• Add a new <React.StrictMode> wrapper to help prepare apps for async rendering. (@bvaughn in #12083)
• Add support for onLoad and onError events on the <link> tag. (@roderickhsiao in #11825)
• Add support for noModule boolean attribute on the <script> tag. (@aweary in #11900)
• Fix minor DOM input bugs in IE and Safari. (@nhunzaker in #11534)
• Correctly detect Ctrl + Enter in onKeyPress in more browsers. (@nstraub in #10514)
• Fix containing elements getting focused on SSR markup mismatch. (@koba04 in #11737)
• Fix value and defaultValue to ignore Symbol values. (@nhunzaker in #11741)
• Fix refs to class components not getting cleaned up when the attribute is removed. (@bvaughn in #12178)
• Throw with a meaningful message if the component runs after jsdom has been destroyed. (@gaearon in #11677)
• Don't crash if there is a global variable called opera with a null value. @alisherdavronov in #11854)
• Don't check for old versions of Opera. (@skiritsis in #11921)
• Deduplicate warning messages about <option selected>. (@watadarkstar in #11821)
• Deduplicate warning messages about invalid callback. (@yenshih in #11833)
• Deprecate ReactDOM.unstable_createPortal() in favor of ReactDOM.createPortal(). (@prometheansacrifice in #11747)
• Don't emit User Timing entries for context types. (@abhaynikam in #12250)
• Improve the error message when context consumer child isn't a function. (@raunofreiberg in #12267)
• Improve the error message when adding a ref to a functional component. (@skiritsis in #11782)

React DOM Server

• Prevent an infinite loop when attempting to render portals with SSR. (@gaearon in #11709)
• Warn if a class doesn't extend React.Component. (@wyze in #11993)
• Fix an issue with this.state of different components getting mixed up. (@sophiebits in #12323)
• Provide a better message when component type is undefined. (@HeroProtagonist in #11966)

React Test Renderer

• Fix handling of fragments in toTree(). (@maciej-ka in #12107 and @gaearon in #12154)
• Shallow renderer should assign state to null for components that don't set it. (@jwbay in #11965)
• Shallow renderer should filter legacy context according to contextTypes. (@koba04 in #11922)
• Add an unstable API for testing asynchronous rendering. (@acdlite in #12478)

React Is (New)

• First release of the new package that libraries can use to detect different React node types. (@bvaughn in #12199)
• Add ReactIs.isValidElementType() to help higher-order components validate their inputs. (@jamesreggio in #12483)

React Lifecycles Compat (New)

• First release of the new package to help library developers target multiple versions of React. (@bvaughn in #12105)

Create Subscription (New)

• First release of the new package to subscribe to external data sources safely for async rendering. (@bvaughn in #12325)

React Reconciler (Experimental)

• Expose react-reconciler/persistent for building renderers that use persistent data structures. (@gaearon in #12156)
• Pass host context to finalizeInitialChildren(). (@jquense in #11970)
• Remove useSyncScheduling from the host config. (@acdlite in #11771)

React Call Return (Experimental)

• Fix a crash on updates. (@rmhartog in #11955)