react-native-performance
Optimize React Native rendering for smooth 60fps mobile experiences. Use when optimizing React Native app performance, reducing re-renders, or fixing frame drops.
What this skill does
# React Native Performance ## **Priority: P0 (CRITICAL)** ## Tune FlatList for 60fps - **`windowSize`**: **Reduce to 5-10** for memory-heavy lists (default 21). **`initialNumToRender`** should cover first viewport. - **`getItemLayout`**: Provide for **fixed-height items**. Skips runtime measurement. - **`removeClippedSubviews`**: Enable for **Android** (default true) to offload clipped items. - **`maxToRenderPerBatch`**: Limit to **5-10 items per frame** to prevent JS thread blockage. - **`keyExtractor`**: Use **stable unique IDs**, never array index. See [optimization guide](references/optimization-guide.md) for FlatList configuration examples with `getItemLayout`, `windowSize`, and memoization patterns. ## Accelerate Core Rendering - ** Engine**: Ensure **Hermes engine** enabled (default in 0.7x). Verify via `global.HermesInternal`. - **Animations**: Use **Native Driver (`useNativeDriver: true`)** or **Reanimated 3** for GPU-accelerated 60fps animations. - **Re-renders**: Use **`React.memo`** and **`useMemo`** for expensive props. **Profile via Flipper** (React DevTools) for flamegraphs. - **Network**: Batch API calls. Use **React Query/Zustand** to prevent unnecessary screen refreshes. - **Images**: Use **`react-native-fast-image`** for caching and priority. Avoid large PNGs; use **WebP**. ## Reduce Bundle and Startup Time - **Hermes**: Enable for faster startup (default in RN 0.70+). - **Tree Shaking**: Remove unused imports. - **ProGuard/R8**: Enable code shrinking on Android. - **Lazy Screens**: Use `lazy` prop for stack screens (enabled by default). ## Anti-Patterns - **No ScrollView for Large Lists**: Use FlatList. - **No Inline Styles**: Use `StyleSheet.create` (optimized). - **No console.log in Production**: Strip with babel plugin. ## References See [references/optimization-guide.md](references/optimization-guide.md) for FlatList configuration, memoization rules, and bundle analysis.
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