⏱ Rename Priority Levels

The Core team also made small changes to some of the API names for the scheduler - one of the building blocks of React’s upcoming concurrent mode. The API is not final and we can expect an RFC soon.

https://github.com/facebook/react/pull/13842

🕵️‍♀️ Deprecate findDOMNode in StrictMode

In an attempt to make React applications easier to maintain, the Core team considers deprecating findDOMNode. The current API is breaking abstraction levels which leads to refactoring hazard.

https://github.com/facebook/react/pull/13841

⏪ Revert: React.pure() Automatically Forwards Ref

Last week we were covering a PR that added forwardRef behavior to React.pure() by default. The PR was since reverted while the Core team is working on the future of ref forwarding.

https://github.com/facebook/react/pull/13887

🔥 RFC: React Hooks

The React team announced Hooks - A new and backwards-compatible Component API. In addition to the RFC, the team also launched [a complete set of documentation](https://reactjs.org/docs/hooks-intro.html). You can play around with React Hooks today by using the v16.7.0-alpha release on npm.

https://github.com/reactjs/rfcs/pull/68

🎉 React v16.6.0: lazy, memo and contextType

This week also marks the release of the stable v16.6. This not only adds the lazy, memo, contextType, and getDerivedStateFromError APIs that we covered in previous issues, but is also the first public build where Suspense is no longer behind a feature flag and not marked unstable.

https://reactjs.org/blog/2018/10/23/react-v-16-6.html

⏱ Enable concurrent APIs flag for 16.7

Concurrent APIs (ReactDOM.createRoot and <ConcurrentMode/>) will no longer be unstable in the upcoming v16.7.0 release.

https://github.com/facebook/react/pull/13928

➡️ React.pure() is now React.memo()

After discussions in the RFC that we covered last week, React.pure() is now called React.memo().

https://github.com/facebook/react/pull/13905

📚 Remove cache as argument to read in React Cache

The React Cache API is still unstable and will undergo more changes. The cache is now read from context and cache invalidation was removed entirely. You can try it out in the v2.0.0-alpha.0 release.

https://github.com/facebook/react/pull/13865

🎣 Hooks Merged Into React Master

The implantation of the experimental Hooks proposal landed in React’s master branch this week. The PR contains valuable information on how hooks are implemented.
https://github.com/facebook/react/pull/13968

🔁 Add Back Proper AsyncMode Symbol for Back Compat

Thanks to Jordan Harband (ljharb), the react-is package to test arbitrary values and see if they’re a particular React element type now correctly handles the meanwhile renamed AsyncMode component.
https://github.com/facebook/react/pull/13959

⁉️ Don’t Lint Against Hooks After Conditional Throw

To make working with React Hooks easier, the Core team is working on a linter rule that helps to comply with the Rules of Hooks. This PR takes the custom linter one step forward.
https://github.com/facebook/react/pull/14040

⏳ Flip Expiration Times

In an effort to simplify the reconciler code, internal priority levels now have their values reversed.
https://github.com/facebook/react/pull/13912

⏱ Deadline Object ➡ shouldYield

Instead of using a requestIdleCallback-style deadline object, the Scheduler now expose a shouldYield method that returns true if there’s a higher priority event in the queue.
https://github.com/facebook/react/pull/14025

🐞 Debug Tools Package for Introspection of Hooks

To make it easier to debug React Hooks, the team added a new experimental package for debugging React renderers.

https://github.com/facebook/react/pull/14085

🧠 A Metaphor for Concurrent React

Dan wrote an excellent metaphor for the upcoming concurrent mode in React. Check out his Twitter thread if you’re curious about the mental model behind this upcoming feature.

https://twitter.com/dan_abramov/status/1059059596835340288

🤞 Avoid Double Commit by Re-rendering Immediately

To fix issues when using Suspense in non-concurrent mode, we now render the suspended and the fallback children within a single commit. Andrew also posted a great summary of the PR.

https://github.com/facebook/react/pull/14083

🗄 Suspense Fuzz Tester

A new fuzz tester was added to improve the reliability of suspense. It works by generating random trees of React elements, with some elements that suspend and some that don’t.

https://github.com/facebook/react/pull/14147

⏳ Add a Low Priority to the Scheduler

Nathan Schloss (n8schloss) made a PR to add another priority level to the experimental Scheduler package. This new priority will still resolve but only after everything else. This is useful for logging or sending data back to the server.

https://github.com/facebook/react/pull/14155

🦄 Unify Hooks’ Second Argument Comparison

Thanks to Mateusz Burzyński (Andarist) we now also have development warnings in the server renderer implementation for the second argument comparison implementation of hooks.

https://github.com/facebook/react/pull/14036

✨ Warn for Bad useEffect Return Value

The cleanup function for the useEffect hook must always be returned synchronously, something that’s not possible to do when an async function is used. We now warn in such cases.

https://github.com/facebook/react/pull/14069

🌁 Fix Crash During Server Render in React 16.6

React can be loaded into many JavaScript runtimes. Thanks to Tiago Nunes (tnunes), it can now again be loaded into environments without setTimeout (e.g. ClearScript for .NET).

https://github.com/facebook/react/pull/14103