🐞 New DevTools Architecture Overview

Brian updated the new DevTools Architecture Overview with the goal of minimizing bridge traffic and avoid serialization overhead.

https://github.com/bvaughn/react-devtools-experimental/blob/master/OVERVIEW.md

🚀 Scheduling in React

I wrote an article about why we need Scheduling in React. Make sure to also check out Dan’s comments.

https://philippspiess.com/scheduling-in-react/

🌏 New React Docs Localizations Live

This week, four new React documentation websites went live:
• French: fr.reactjs.org
• Russian: ru.reactjs.org
• Ukrainian: uk.reactjs.org
Simplified Chinese: zh-hans.reactjs.org
At the same time, two new localization repos where added:
• Swedish: reactjs/sv.reactjs.org
• Thai: reactjs/th.reactjs.org

📌 ESLint: Warn about Dependencies Outside of Render Scope

Variables that are defined outside of the render scope (for example global variables like window) do not cause a component to re-render when they’re mutated. This doesn’t play together with the dependency array so the ESLint rule exhaustive-deps now warns in those cases.

https://github.com/facebook/react/pull/14990

⏳ Import Scheduler Directly

With the introduction of a general purpose scheduler, the individual React renders can now directly call the unified Scheduler APIs. Read the PR denoscription for a good overview of the current situation!

https://github.com/facebook/react/pull/14984

⚠️ Warn When Dependencies Are Not an Array

React now warns on mounting a component that uses hooks where the dependencies are not an array.

https://github.com/facebook/react/pull/15018

⚓️ ESLint: Treat Functions That Don’t Capture Anything As Static

For the exhaustive-deps ESLint rule, functions that do not capture anything are now treated as static. Even if they close over a setState() function that comes from the useState() hook.

https://github.com/facebook/react/pull/14996

🎣 ESLint: Enforce Dependencies Array in useMemo and useCallback

The ESLint rule will now also enforce a dependencies array when useMemo() or useCallback() is used.

https://github.com/facebook/react/pull/15025

📌 React v16.8.4 Patch Release

This release includes a bug fix that sometimes caused a runtime error when DevTools are open

https://github.com/facebook/react/releases/tag/v16.8.4

🍱 A Complete Guide to useEffect

Dan wrote another extensive blog post which goes into the nitty gritty details of the useEffect hook. Highly recommended!
https://overreacted.io/a-complete-guide-to-useeffect/

⚠️ Warn for javanoscript: URLs in DOM Sinks

javanoscript: URLs in DOM sinks are a possible attack vector for XSS attacks. This PR adds a warning when using those for the remainder of 16.x releases.
https://github.com/facebook/react/pull/15047

📱 Infrastructure for Passive/Non-Passive Event Experiments

To explore future APIs, this PR is adding infrastructure to allow registration for passive/non-passive events in the event system. Please note that this is currently in the experimentation phase and it might take some time until these APIs are available.
https://github.com/facebook/react/pull/15036

🌎 React Docs Localizations Update

Five new React documentation websites went live:
German: de.reactjs.org
Hebrew: he.reactjs.org
Korean: ko.reactjs.org
Polish: pl.reactjs.org
Turkish: tr.reactjs.org
These websites are now complete:
Portuguese (Brazil): pt-br.reactjs.org
Russian: ru.reactjs.org
In addition to that, we’re happy to welcome the Georgian localization repository.
https://github.com/reactjs/ka.reactjs.org

🚀 Run Persistent Mode Tests in CI

This PR adds a new command to run persisted mode tests in CI as well.
https://github.com/facebook/react/pull/15029

⚓️ Improve Hooks FAQ About Dependencies

To address some frequently asked questions about the dependencies array used for some hooks, this PR adds new content to the documentation.
https://github.com/reactjs/reactjs.org/pull/1815

🏞 Partial Hydration: Render Client-only Content at Normal Priority

This change is improving handling of partially hydrated HTML of server-rendered suspense boundaries.
https://github.com/facebook/react/pull/15061

🧪 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