React Native Performance

Priority: P0 (CRITICAL)

FlatList Optimization

• windowSize: Reduce to 5-10 for long lists (default 21).
• getItemLayout: Provide for fixed-height items. Skips measurement.
• removeClippedSubviews: Enable for Android (default true).
• maxToRenderPerBatch: Limit to 5-10 items per frame.
• keyExtractor: Use stable unique IDs, never index.
• Avoid Anonymous Functions: Define renderItem outside component or use useCallback.

React Optimization

• React.memo: Wrap presentational components to prevent re-renders.
• useMemo: Cache expensive calculations.
• useCallback: Stabilize function refs for child props.
• Avoid Inline Objects: Extract to constants or useMemo.

Navigation

• Lazy Screens: Use lazy prop for stack screens (enabled by default).
• Avoid Listeners: Remove navigation event listeners in cleanup.

Images

• Image Caching: Use react-native-fast-image for network images.
• Resize: Provide resizeMode and fixed dimensions.
• Format: Use WebP for smaller size.

Bundle Size

• Hermes: Enable for faster startup (default in RN 0.70+).
• Tree Shaking: Remove unused imports.
• ProGuard/R8: Enable code shrinking on Android.

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.

Reference & Examples

See references/optimization-guide.md for FlatList configuration, memoization rules, and bundle analysis.

Related Topics

react/performance | common/performance-engineering