Modernizing React Native’s JavaScript

React Native uses view configs to translate JavaScript props into values native components can use, such as converting a color name into an integer. Today, it calculates these configs at app startup through native reflection, even for components the app may never use. White says platform differences and separate native, JavaScript, and documentation definitions also create inconsistent sources of truth.

White describes Codegen as a system that takes Flow or TypeScript definitions, converts them into a shared schema, and generates native interfaces and JavaScript view configs. This makes JavaScript the single source of truth and puts view configs in the app bundle instead of calculating them at runtime. The generated interfaces keep types consistent across JavaScript and native code, including for native modules.

White says Fabric does not use UIManager, and direct product code calls to it are being deprecated. For measuring a view, he points to the existing `ref.measure` API; for component commands such as `scrollTo` or a map’s `moveToRegion`, Codegen can generate typed methods and matching native interfaces. This replaces untyped command arguments passed in arrays.

`findNodeHandle` searches for the nearest native component behind a JavaScript ref, so a seemingly simple refactor, such as adding or removing a wrapper view, can change what gets measured. White says the search is slow and requires maintaining the React tree. He recommends forwarding refs to the intended native view, then calling methods such as `measure` on that ref; React Native core components in version 0.62 already use `forwardRef`.

White frames the removals as changes to uncommon features, often used in library code, and says the aim is to keep application code working with as few changes as possible. UIManager access and `findNodeHandle` are slated for deprecation, with migration guidance and replacement APIs planned for supported use cases.