🔄 Support Sync Thenables for lazy()

You can now pass a synchronous thenable (an object where the then property callback is executed synchronously) into lazy().
https://github.com/facebook/react/pull/14626

✌️ Warn When Passing Second Callback to setState/dispatch in Hooks

In class components, you can pass in a second callback to this.setState() that is run when the update is applied. When using hooks, this is not supported.
https://github.com/facebook/react/pull/14625

🛑 Disallow Reading Context During useMemo, etc.

The callback functions of useMemo, use(Layout)Effect, useReducer, and useState can no longer read context by accessing the internal dispatcher.
https://github.com/facebook/react/pull/14653

🌏 reactjs.org Internationalization Using Forks

With the big help of Nat Alison (tesseralis) and the community, we’re starting to internationalize the official React documentation using forks of the english repository. Want to get involved? Check out the three initial forks:
Simplified Chinese: reactjs/zh-hans.reactjs.org
Spanish: reactjs/es.reactjs.org
Japanese: reactjs/ja.reactjs.org

https://github.com/reactjs/reactjs.org/issues/1605

☯️ Phased Dispatcher

The hooks module was refactored to use separate dispatchers for the mount and update phases. This speeds up initial render by removing update-only branches from the hot path.

https://github.com/facebook/react/pull/14701

🏞 WIP: Partial Hydration

The Core team is working on a new partial hydration mode that can start hydrating a server rendered result while some parts are still loading. The goal is decrease the time to interactive.

https://github.com/facebook/react/pull/14717

📚 useReducer Lazy Initialization API

The useReducer API to lazily initialize the state was changed so you can provide an initializer function instead of initial actions that had to be handled in the reducer itself.

https://github.com/facebook/react/pull/14723

📌 Warn When Second Argument Is Passed to useContext

In the initial alpha version, the second argument to useContext could be used to set the observedBits. React now warns when a second argument is passed and the team can thus change the meaning later.

https://github.com/facebook/react/pull/14729

🎉 React v16.8: The One With Hooks

Three month after the initial reveal of React Hooks at React Conf 2018, this new feature is now part of the latest stable release. If you haven’t heard of hooks before, check out the official documentation.

https://reactjs.org/blog/2019/02/06/react-v16.8.0.html

🌏 Is React Translated Yet?

You can now track the status of the React documentation translation effort on this new website: https://www.isreacttranslatedyet.com/

🌍 New React Internationalization Repos

This week, eight new internationalization repositories were created. Your language is not listed? Get involved!
Azerbaijani: reactjs/az.reactjs.org
French: reactjs/fr.reactjs.org
Indonesian: reactjs/id.reactjs.org
Korean: reactjs/ko.reactjs.org
Portuguese (Brazil): reactjs/pt-BR.reactjs.org
Russian: reactjs/ru.reactjs.org
Traditional Chinese: reactjs/zh-hant.reactjs.org
Vietnamese: reactjs/vi.reactjs.org

https://github.com/reactjs/reactjs.org-translation

🧪 Add ReactTestRenderer.act() and ReactTestUtils.act()

Two new test helpers are now available for batching updates so that tests more closely match the real behavior.

https://github.com/facebook/react/pull/14744

⏰ Scheduler.unstable_next()

A new unstable API was added to the Scheduler to queue a task with a lower priority than the default priority of interaction callbacks. This allows CPU or IO-heavy work to run after the UI responds.

https://github.com/facebook/react/pull/14756

⏮ Backwards Compat Fix for ReactCurrentDispatcher

A previous pull request caused issues when combining newer renderers with a version of the react package that predated the change. This is now fixed.

https://github.com/facebook/react/pull/14770

📌 React v16.8.1 Patch Release

After the big v16.8 release, the team also worked on some smaller bug fixes which are now out as well. Thank you for your hard work!

https://github.com/facebook/react/blob/master/CHANGELOG.md#1681-february-6-2019

☕️ React as a UI Runtime

In this comprehensive article, Dan (@gaearon) wrote a lot about the internals of React. I highly recommend this read: https://overreacted.io/react-as-a-ui-runtime/

🏞 Partial Hydration

The partial hydration PR has now landed in master. This new mode can start hydrating a server rendered result while some parts are still loading. The goal is decrease the time to interactive.

https://github.com/facebook/react/pull/14717

📚 Component Stack in act() Warning

The warning about missing act() wrapping in some test environments now contains a component stack trace.

https://github.com/facebook/react/pull/14855

🖥 Fix SSR Context Leaks When Render Stream Destroyed Early

This PR fixes a Context memory leak in the SSR if a stream is destroyed before the render completes.

https://github.com/facebook/react/pull/14706

📡 Properly Support crossOrigin for SVG Images

We now properly case the crossOrigin property that’s used for SVG image elements.

https://github.com/facebook/react/pull/14832

👀 Fix useImperativeHandle Without Dependencies

The useImperativeHandle hook now properly behaves like no dependencies were set when the second argument is omitted.

https://github.com/facebook/react/pull/14801

📌 React v16.8.2 Patch Release

This release brings bug fixes and stability improvements around hooks and other features.

https://github.com/facebook/react/blob/master/CHANGELOG.md#1682-february-14-2019