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REACT NATIVE CLEANS HOUSE, JEST REVERTS WATCHER EXPERIMENT
By RepoJournal · Filed · About Meta · Composed from the cited sources · methodology
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React Native dropped deprecated DisplayMetrics APIs while Jest pulled the plug on a half-baked watcher backend, then pivoted to consolidate file traversal into a single shared implementation.
React Native shipped the removal of `getWindowDisplayMetrics` and related DisplayMetricsHolder APIs [1], finally closing out a deprecation cycle that's been sitting on the books since 0.87. If you're still calling these methods on Android, your builds will break on next upgrade. Jest had a rougher day. The team merged a new `haste.backend` option to support Parcel watcher [3], then immediately reverted it [3] after realizing the implementation wasn't ready for production. That's the right call, but it signals internal friction on the file-watching strategy. What's shipping instead is a cleaner win: consolidating Jest's two hand-rolled directory walkers and the separate `walker` npm dependency into a single `fdir`-based implementation [2]. This removes duplicate traversal logic across `crawlers/node.ts`, `watchers/common.js`, and `FSEventsWatcher.ts`, cutting maintenance surface and likely improving performance.
Action items
- → Update Android code calling DisplayMetricsHolder.getWindowDisplayMetrics before next React Native upgrade facebook/react-native [plan]
- → Monitor Jest's next release for the fdir consolidation and test file watching in your CI environment facebook/jest [monitor]
References
- [1] Remove getWindowDisplayMetrics from DisplayMetricsHolder (#56635) ↗ facebook/react-native
- [2] chore(haste-map): replace `walker` and hand-rolled traversal with `fdir` ↗ facebook/jest
- [3] Revert "feat(haste-map): add haste.backend option (#16184)" ↗ facebook/jest
