⏳ Measure Callback Timeout Relative to Current Time

This PR fixes an issue with the new ReactFiberScheduler by measuring the callback timeout relative to the current time.

https://github.com/facebook/react/pull/15479

🎉 DevTools Beta: Component Filters

The experimental rewrite of the React DevTools now comes with an option to filter components based on their name, type, or location.

Pressing the filter button in the new DevTools shows you options to filter components by name, type, and location.

https://twitter.com/brian_d_vaughn/status/1123765242767597576

🎇 React Flare: onFocusVisibleChange

Adds the new onFocusVisibleChange API to the Focus element. This event will only dispatch if the focus was triggered by a keyboard.

https://github.com/facebook/react/pull/15516

⏱ Scheduler: Forcing Low Framerate

A new Scheduler API allows forcing of lower frame rates. This is useful especially on lower spec devices that may not run enough tasks within the default frame budget.

https://github.com/facebook/react/pull/14826

🌍 React Docs Localizations Updates

The Polish localization is now complete!

https://pl.reactjs.org/

🎇 React Flare Updates

In addition to the onFocusVisibleChange API, all experimental event API listeners now use the capture phase, isTargetDirectlyWithinEventComponent was removed, and bugs were fixed.

https://github.com/facebook/react/pull/15526
https://github.com/facebook/react/pull/15546
https://github.com/facebook/react/pull/15514

📘 Building the New Facebook.com

At F8 this week, the new Facebook.com was revealed. This talk takes a deep dive into the new UI architecture and explains how the latest React features are used to build a high quality user experience.

https://developers.facebook.com/videos/2019/building-the-new-facebookcom-with-react-graphql-and-relay

🕳 Add Suspense Boundary Context and unstable_avoidThisFallback

The new suspense boundary context will be used to implement longer suspense in case it is undesirable to show a certain fallback state.
The first usage of this is the unstable_avoidThisFallback property that can be used to avoid fall back to the outer most suspense boundary.

https://github.com/facebook/react/pull/15578

🛠 Experimental DevTools: Add Suspense Toggle to All Elements

You can now toggle suspense on every element in the experimental DevTools. If the component is not in a suspense boundary, it will also show a warning.

https://twitter.com/brian_d_vaughn/status/1126182658864599040

⚠️ Warn When Suspending at Wrong Priority

This change adds a warning when components suspend during a user-blocking update. The warning recommends to schedule suspending updates via Scheduler.next instead.

https://github.com/facebook/react/pull/15492

🎇 React Flare Updates

Continuing the work of the past few weeks, the team worked on adding React.unstable_createEventComponent, more press event properties, server-side hit slop rendering, and a lot of other bug fixes.

https://github.com/facebook/react/issues/15257

🎽 Fix Interaction Tracing for Batched Update Mounts

This PR fixes an issue with interaction tracking that occurred when a root was mounting inside a batched update.

https://github.com/facebook/react/pull/15567

🔋 Batched Mode and

ReactDOM.unstable_createSyncRoot
Batched Mode is a new unstable React mode that ensures that updates are always batched while still doing all rendering without interruption. It can be opted in with the new ReactDOM.unstable_createSyncRoot API.

https://github.com/facebook/react/pull/15502

🌀 Add withSuspenseConfig API

The new unstable_withSuspenseConfig() API can be used to schedule updates with a different suspense config. This can be used to implement busy spinners.

https://github.com/facebook/react/pull/15593

👋 Remove <React.unstable_ConcurrentMode />

Partial opt-in into Concurrent Mode creates edge cases that are not trivial to support. Instead, the recommended approach is to opt in the entire root.

https://github.com/facebook/react/pull/15532

🧪 Flush the Scheduler Manually inside act()

With this PR, the act() test helper is now manually flushing the Scheduler using Scheduler.unstable_flushWithoutYielding internally.

https://github.com/facebook/react/pull/15591

🕹 Fix Serial Passive Effects

This change makes sure that passive effects are flushed before discrete event handlers are called.

https://github.com/facebook/react/pull/15650

⏲ Remove Scheduler from React Package Dependencies

The isomorphic react package no longer depends directly on the scheduler. Now, only the individual renderers (e.g. react-dom) do.

https://github.com/facebook/react/pull/15616

🙅‍♀️ Invariant When Committing Wrong Tree

This change adds a new invariant that throws if the new tree is the same as the old one.

https://github.com/facebook/react/pull/15517

🎇 React Flare Updates

Another week of great improvements for the experimental event API that the team at Facebook is working on. preventDefault now work for nested updates, a pointerType was added to to Focus events, getFocusableElementsInScope handles suspended trees, and more.

https://github.com/facebook/react/issues/15257

🛑 Bail out of Updates in Offscreen Trees

With this change, sync updates inside hidden trees are now delayed when using Concurrent Mode.

https://github.com/facebook/react/pull/15666