---

name: mobile-perf description: Optimizes React Native Expo applications for speed, responsiveness, and battery efficiency. Use when fixing lag, optimizing lists, or reducing bundle size.

Mobile Performance Skill

This skill focuses on delivering a "butter-smooth" user experience.

Focus Areas

• List Optimization: Use LegendList or highly optimized FlatList settings.
• Animation Performance: Ensure all animations run on the UI thread using react-native-reanimated.
• Image Handling: Use expo-image for caching and performant loading.
• JS Bundle Size: Analyze and reduce the size of the JavaScript bundle.
• Memory Leaks: Identify and fix component memory leaks or excessive re-renders.

Instructions

1. Profile: Identify the bottleneck (JS thread vs UI thread).
2. Optimize Lists: Use removeClippedSubviews, maxToRenderPerBatch, and initialNumToRender.
3. Memoization: Apply useMemo and useCallback judiciously to prevent unnecessary renders.
4. Bridge Traffic: Minimize the data sent across the React Native bridge.

Recommended Tools

• Flashlight for performance testing.
• react-devtools for profiling renders.
• expo-bundle-analyzer to check bundle composition.