🧪 Experimental Event API Scaffolding

To experiment with new event APIs, this PR adds some scaffolding to React and adds new Event primitives.
https://github.com/facebook/react/pull/15108

🔥 React.warn() and React.error()

This PR adds two new APIs to React: React.warn() and React.error(). These will log to the console and include a component stack. Useful for providing more detailed error messages in third party packages.
https://github.com/facebook/react/pull/15170

🎉 Stable Profiler API

The profiler API, added about 10 month ago, is now marked as stable.
https://github.com/facebook/react/pull/15172

👋 Deprecate Module Pattern Components

Module pattern components take a fairly complex code path in React but are barely used outside of a few special places (like Relay Classic). This PR deprecates this pattern as also outlined in the RFC about createElement changes.
https://github.com/facebook/react/pull/15145

➡️ Shallow Renderer: Support React.memo()

React.memo() can now be used in the shallow renderer.
https://github.com/facebook/react/pull/14816

🌍 React Docs Localizations Updates

Simplified Chinese is now complete:
zh-hans.reactjs.org
The Italian documentation websites went live:
it.reactjs.org
In addition to that, we’re happy to welcome the Kannada localization repository.
https://github.com/reactjs/kn.reactjs.org

💊 Safely Access Cross-Origin Iframes

This contribution fixes an issue in Safari where a focused element within a cross-origin iframe caused an error to be always logged.
https://github.com/facebook/react/pull/15099

⚠️ ESLint: Warn About setState Directly in Dep-less useEffect

The ESLint rule for hooks now warns when setState is called without defining dependencies. This could easily lead to loops. This change is already out in eslint-plugin-react-hooks@1.6.0.
https://github.com/facebook/react/pull/15184

🏠 Compile Invariant Directly to Throw Expressions

React uses invariant() to assert correct behavior. In production, the error message is stripped out to keep the bundle size down. This PR reworks how this is handled.
https://github.com/facebook/react/pull/15071

🌅 Shallow Renderer: Implement setState for Hooks

The shallow renderer now supports calling the setState updater of useState() hooks outside of the render function.
https://github.com/facebook/react/pull/15120

📖 Docs: How Can I Measure a DOM Node?

The React Hooks FAQs now contain a new entry with information on how to best measure DOM nodes.
https://reactjs.org/docs/hooks-faq.html#how-can-i-measure-a-dom-node

🖱 Internal Event API Experiments Updates

While working on internal experiments for a new event API, the Core team added more scaffolding, a new react-events package, and logic for listening to event responders.
https://github.com/facebook/react/pull/15168

⛑ Add Feature Flag to Disable Yielding

A new feature flag was added that allows debug builds to disable yielding in Concurrent Mode.
https://github.com/facebook/react/pull/15119

📌 React v16.8.5 Patch Release

This release includes a improved warnings and support for newer features in the shallow renderer.
https://github.com/facebook/react/releases/tag/v16.8.5

🕹 Internal Event API Experiments Updates

This week added more parts to the internal event API experiments including event component responder surfaces and SSR support.

https://github.com/facebook/react/pull/15179

💃 Dancing Between State and Effects

James Long (jlongster) started a discussion about ways to combine effects and state changes. Feedback welcome!

https://github.com/facebook/react/issues/15240

🎚 Enabled warnAboutDeprecatedLifecycles

React will, starting with the next minor version, warn when deprecated lifecycle methods are used. You can learn more about this deprecation in this blog post.

https://reactjs.org/blog/2018/03/27/update-on-async-rendering.html

https://github.com/facebook/react/pull/15186

🌍 Turkish Localization Completed

The Turkish localization is now complete, making it the eight complete localization.

https://tr.reactjs.org/

⚠️ Warn About Async Infinite useEffect loop

This PR adds a warning for an infinite useEffect loop caused by calling setState without defining a dependency array or one of the dependencies changes on every render.

https://github.com/facebook/react/pull/15180

📌 React v16.8.6 Patch Release

This release includes a fix for useReducer() bailout and a fix for cross-origin iframes in Safari as well as two new warnings related to contextType.

https://github.com/facebook/react/releases/tag/v16.8.6

💙 Rachel Nabors Joining the React Core Team

Rachel Nabors (rachelnabors) will join the React Core team in May and will be writing docs, building demos, and tending the community. I can’t be more excited!

https://twitter.com/rachelnabors/status/1112699525528018945