From Lag to Lightning: Boosting React Native Performance

Hermes is a JavaScript engine designed for React Native that pre-compiles JavaScript into bytecode, reducing runtime parsing time. It optimizes garbage collection and can significantly cut cold start times, especially on Android.

Common bottlenecks include the single-threaded nature of JavaScript, inefficient use of FlatList, frequent re-renders due to prop state changes, blocking API calls, and large payloads overwhelming the React Native bridge.

To optimize FlatList, use props like initialNumToRender and maxToRenderPerBatch to control rendering. Memoize the renderItem function to avoid unnecessary re-renders and improve performance.

Cleaning up side effects, such as removing listeners, timers, and subscriptions, is crucial to prevent memory leaks, which can degrade performance over time.

The new architecture features JSI (JavaScript Interface), fabric renderer, and turbo modules, which replace the bridge, allowing direct synchronous communication and unlocking significant performance improvements.

Animations should use the native driver to run on the native thread instead of the JS thread, ensuring smooth performance even during heavy processing. Set useNativeDriver to true for this optimization.

Performance is crucial because 53% of users abandon an app if it takes longer than three seconds to load, and 80% abandon apps that lag or crash. Poor performance can also lead to reduced conversion rates, user churn, plummeting app ratings, and revenue loss.

To maintain smooth performance, apps should run at 60 frames per second (FPS). Dropping below 30 FPS can cause users to notice lag, affecting engagement and retention.

Recommended profiling tools include Flipper, Chrome Dev Tools, React Dev Tools, Xcode Instruments, and Android Profiler. These tools help identify performance bottlenecks and optimize app performance.