React Native allows developers to build mobile apps using JavaScript. However, bridging JavaScript code with native UI components can occasionally introduce frame drops and touch delay.
This guide explains how to leverage the Hermes engine and bridge profiling tools to build highly performant React Native applications.
1. Enabling and Optimizing Hermes
Hermes is an open-source JavaScript engine optimized for running React Native. It compiles JavaScript code into bytecode at build time, lowering app startup times.
- Bytecode precompilation: Ensures the engine doesn't parse code on startup.
- Garbage Collection Tuning: Uses an active, concurrent GC to prevent frame drops during rendering.
2. Profiling the Native Bridge
In older React Native architectures, all data exchange between JavaScript and native threads must traverse the "Bridge". Heavy payloads (like base64 images or massive arrays) can saturate this bridge, blocking UI interactions.
- Minimize Serializations: Pass references or identifiers across the bridge instead of full objects.
- Transition to JSI (New Architecture): Adopt the new architecture (TurboModules and Fabric) to allow JavaScript to directly invoke native functions without serialization overhead.