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name: react-native-best-practices description: React Native performance optimization guidelines from Callstack's Ultimate Guide. Use this skill when writing, reviewing, or debugging React Native code for performance issues. Triggers on tasks involving FPS optimization, TTI improvement, bundle size reduction, native module development, memory leaks, or animation performance.

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

Priority	Category	Impact	Prefix
1	FPS & Re-renders	CRITICAL	js-*
2	Bundle Size	CRITICAL	bundle-*
3	TTI Optimization	HIGH	native-*, bundle-*
4	Native Performance	HIGH	native-*
5	Memory Management	MEDIUM-HIGH	js-*, native-*
6	Animations	MEDIUM	js-*

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

Problem	Start With
App feels slow/janky	js-measure-fps.md → js-profile-react.md
Too many re-renders	js-profile-react.md → js-react-compiler.md
Slow startup (TTI)	native-measure-tti.md → bundle-analyze-js.md
Large app size	bundle-analyze-app.md → bundle-r8-android.md
Memory growing	js-memory-leaks.md or native-memory-leaks.md
Animation drops frames	js-animations-reanimated.md
List scroll jank	js-lists-flatlist-flashlist.md
TextInput lag	js-uncontrolled-components.md
Native module slow	native-turbo-modules.md → native-threading-model.md

Attribution

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