The New React Native

Janzer says the team is testing the new architecture in production at Facebook to find bugs before releasing it to the open-source community. The plan has three phases: a type-safe native module system, a new renderer, and a faster initialization path. At the time of the talk, the team expected the first pieces to reach developers in early 2020.

The new native module system, called TurboModules, aims to improve type safety, reduce call overhead, and initialize modules only when needed. Fabric is a C++ rewrite of the UI layer that supports synchronous layout and measurement, which Janzer says could improve native integration and components such as TextInput and ScrollView. Both were being tested at Facebook, with releases planned for 2020.

React Native’s existing bridge sends messages asynchronously in batches and serializes objects as JSON. Janzer says this adds overhead, especially for large objects. The new architecture uses JavaScript Interface, or JSI, to let C++ and JavaScript call functions and access JavaScript objects more directly.

The planned initialization path removes bridge setup and other work the new architecture no longer needs. Janzer says lazy native module initialization had improved startup by about 400 milliseconds at Facebook. The team also planned to move some setup, including timer and error handling, from JavaScript into C++ so it could happen before JavaScript runs.

Janzer says the architecture aims to improve native interop, performance, reliability, and type safety, while supporting future capabilities such as Concurrent Mode. Developers need not wait for it to improve their apps: she recommends fetching data in parallel with startup, enabling Hermes on Android, and using Flow or TypeScript. She also asks developers to share feedback, especially about brownfield apps and other platforms.