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)
• Fix an IE/Edge issue when rendering inputs into a different window. (@M-ZubairAhmed in #11870)
• 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)