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The Wire · Showcase

REACT SHIPS STYLESHEET PRELOAD FIX, JEST 30.4 REWRITES RUNTIME FOR ESM STABILITY

By RepoJournal · Filed · About Meta

React's Fiber engine now correctly tracks explicitly preloaded stylesheets, eliminating unnecessary commit suspensions that plagued stylesheet-heavy apps, while Jest's massive 30.4 release stabilizes ESM support and adds Temporal API mocking for Node 26.

The stylesheet preload fix [1] lands in React as a critical stabilization — previously preloaded stylesheets would force Fiber to re-request the same resource, delaying commits or triggering fallbacks even when the asset was already loading. This matters for any app using resource hints in the document head. On the React Native side, the team is aggressively cleaning house: removing the deprecated websocketProxyURL property [2], excising the unused LIS differentiator experiment flag [3], and completing the z-index deprecation [4]. A new RFC [5] proposes replacing the ambiguous 'unspecified' value with 'auto' in ColorScheme APIs, aligning with CSS standards. Meanwhile, Jest 30.4 [6] lands a complete runtime rewrite that unblocks native ESM stabilization — you can now `require(esm)` on Node 24.9+ (still experimental), React 19 snapshots finally work correctly in pretty-format, and fake timers now mock the Temporal API for Node 26 compatibility. Two critical Jest bugs got fixed: coverage reports now work properly with the `projects` option [7], and global coverage thresholds apply correctly to unmatched pattern files [8].

Action items

References

  1. [1] [Fiber] track stylesheet preloads when explicitly preloaded ↗ facebook/react
  2. [2] Remove unused websocketProxyURL property (#56722) facebook/react-native
  3. [3] Cleanup useLISAlgorithmInDifferentiator flag (#56715) facebook/react-native
  4. [4] Remove setViewZIndex and associated state from BaseViewManager (#56717) facebook/react-native
  5. [5] Add 'auto' to ColorSchemeOverride, deprecate 'unspecified' facebook/react-native
  6. [6] v30.4.0 ↗ facebook/jest
  7. [7] fix: make coverage work when using `projects` option ↗ facebook/jest
  8. [8] fix(jest-reporters): apply global coverage threshold to unmatched pattern files ↗ facebook/jest

FAQ

What changed in Meta on May 8, 2026?
React's Fiber engine now correctly tracks explicitly preloaded stylesheets, eliminating unnecessary commit suspensions that plagued stylesheet-heavy apps, while Jest's massive 30.4 release stabilizes ESM support and adds Temporal API mocking for Node 26.
What should Meta teams do about it?
Upgrade React to pick up stylesheet preload tracking — test apps with resource hints in strict mode • Upgrade Jest to 30.4 if you're on Node 26 or using Temporal mocking — snapshot tests will improve • Audit React Native code for deprecated zIndex and websocketProxyURL usage before next major
Which Meta repositories shipped on May 8, 2026?
facebook/react, facebook/react-native, facebook/jest

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