React Native Best Practices

Overview

Performance optimization guide for React Native applications, covering JavaScript/React, Native (iOS/Android), and bundling optimizations. Based on Callstack's "Ultimate Guide to React Native Optimization".

When to Apply

Reference these guidelines when:

• •Debugging slow/janky UI or animations
• •Investigating memory leaks (JS or native)
• •Optimizing app startup time (TTI)
• •Reducing bundle or app size
• •Writing native modules (Turbo Modules)
• •Profiling React Native performance
• •Reviewing React Native code for performance

Priority-Ordered Guidelines

Quick Reference

Critical: FPS & Re-renders

Profile first:

# Open React Native DevTools
# Press 'j' in Metro, or shake device → "Open DevTools"

Common fixes:

• •Replace ScrollView with FlatList/FlashList for lists
• •Use React Compiler for automatic memoization
• •Use atomic state (Jotai/Zustand) to reduce re-renders
• •Use useDeferredValue for expensive computations

Critical: Bundle Size

Analyze bundle:

npx react-native bundle \
  --entry-file index.js \
  --bundle-output output.js \
  --platform ios \
  --sourcemap-output output.js.map \
  --dev false --minify true

npx source-map-explorer output.js --no-border-checks

Common fixes:

• •Avoid barrel imports (import directly from source)
• •Remove unnecessary Intl polyfills (Hermes has native support)
• •Enable tree shaking (Expo SDK 52+ or Re.Pack)
• •Enable R8 for Android native code shrinking

High: TTI Optimization

Measure TTI:

• •Use react-native-performance for markers
• •Only measure cold starts (exclude warm/hot/prewarm)

Common fixes:

• •Disable JS bundle compression on Android (enables Hermes mmap)
• •Use native navigation (react-native-screens)
• •Defer non-critical work with InteractionManager

High: Native Performance

Profile native:

• •iOS: Xcode Instruments → Time Profiler
• •Android: Android Studio → CPU Profiler

Common fixes:

• •Use background threads for heavy native work
• •Prefer async over sync Turbo Module methods
• •Use C++ for cross-platform performance-critical code

References

Full documentation with code examples in references/:

JavaScript/React (js-*)

• •js-profile-react.md - React DevTools profiling
• •js-measure-fps.md - FPS monitoring
• •js-memory-leaks.md - JS memory leak hunting
• •js-lists-flatlist-flashlist.md - List performance
• •js-atomic-state.md - Jotai/Zustand patterns
• •js-concurrent-react.md - useDeferredValue, useTransition
• •js-react-compiler.md - Automatic memoization
• •js-animations-reanimated.md - Reanimated worklets
• •js-uncontrolled-components.md - TextInput optimization

Native (native-*)

• •native-platform-setup.md - iOS/Android tooling guide
• •native-profiling.md - Xcode/Android Studio profiling
• •native-measure-tti.md - TTI measurement setup
• •native-memory-patterns.md - C++/Swift/Kotlin memory
• •native-threading-model.md - Turbo Module threads
• •native-view-flattening.md - View hierarchy debugging
• •native-sdks-over-polyfills.md - Native vs JS libraries
• •native-turbo-modules.md - Building fast native modules
• •native-memory-leaks.md - Native memory leak hunting

Bundling (bundle-*)

• •bundle-analyze-js.md - JS bundle visualization
• •bundle-analyze-app.md - App size analysis
• •bundle-library-size.md - Evaluate dependencies
• •bundle-barrel-exports.md - Avoid barrel imports
• •bundle-tree-shaking.md - Dead code elimination
• •bundle-code-splitting.md - Re.Pack code splitting
• •bundle-r8-android.md - Android code shrinking
• •bundle-native-assets.md - Asset catalog setup
• •bundle-hermes-mmap.md - Disable bundle compression

Searching References

# Find patterns by keyword
grep -l "reanimated" references/
grep -l "flatlist" references/
grep -l "memory" references/
grep -l "profil" references/
grep -l "tti" references/
grep -l "bundle" references/

Problem → Skill Mapping

Attribution

Based on "The Ultimate Guide to React Native Optimization" by Callstack.