React Native Best Practices

Performance optimization guide for React Native applications 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

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

Problem → Solution Mapping

Problem	Start With
App feels slow/janky	Measure FPS → Profile React
Too many re-renders	Profile React → React Compiler
Slow startup (TTI)	Measure TTI → Analyze bundle
Large app size	Analyze app → Enable R8
Memory growing	Check JS or native memory leaks
Animation drops frames	Use Reanimated worklets
List scroll jank	Use FlatList/FlashList
TextInput lag	Use uncontrolled components
Native module slow	Turbo Modules → Threading

Key Patterns

Use FlashList for Large Lists

// Bad: ScrollView with many items
<ScrollView>
  {items.map(item => <Item key={item.id} {...item} />)}
</ScrollView>

// Good: FlashList with virtualization
import { FlashList } from "@shopify/flash-list";

<FlashList
  data={items}
  renderItem={({ item }) => <Item {...item} />}
  estimatedItemSize={100}
/>

Avoid Barrel Imports

// Bad: imports entire barrel
import { Button, Card, Modal } from '@/components';

// Good: direct imports
import { Button } from '@/components/Button';
import { Card } from '@/components/Card';

Use Reanimated for Smooth Animations

import Animated, { 
  useAnimatedStyle, 
  withSpring 
} from 'react-native-reanimated';

const animatedStyle = useAnimatedStyle(() => ({
  transform: [{ scale: withSpring(pressed.value ? 0.9 : 1) }],
}));

Defer Non-Critical Work

import { InteractionManager } from 'react-native';

useEffect(() => {
  InteractionManager.runAfterInteractions(() => {
    // Expensive work after animations complete
    loadAnalytics();
  });
}, []);

Attribution

Based on "The Ultimate Guide to React Native Optimization" by Callstack - 642+ installs.