React Native Expert - Setup, Build, Debug, Performance

Comprehensive React Native and Expo expertise covering environment setup, Metro bundler, native modules, device testing, performance optimization, and debugging.

Quick Setup Commands

Expo (Recommended)

# Create new project
npx create-expo-app@latest MyProject
cd MyProject
npx expo start

# Development build (custom native code)
npx expo install expo-dev-client
eas build --profile development --platform ios

React Native CLI

# Create project (New Architecture enabled by default)
npx @react-native-community/cli init MyProject
cd MyProject

# Install iOS deps with New Architecture
cd ios && RCT_NEW_ARCH_ENABLED=1 pod install && cd ..

# Run
npm run ios
npm run android

Environment Requirements (2025)

Component	Minimum	Recommended
Node.js	20.x	22 LTS
React Native	0.76+	0.83
Expo SDK	52+	54
Xcode	16.1	26
Android SDK	34	35
CocoaPods	1.14	1.15+

Common Build Issues

Metro Cache Issues

# Clear everything
watchman watch-del-all
npx react-native start --reset-cache

# Expo
npx expo start --clear

iOS Pod Issues

# Nuclear option
cd ios && rm -rf build Pods Podfile.lock && pod install && cd ..

Android Gradle Issues

cd android && ./gradlew clean && cd ..

Native Modules

Creating Turbo Module

// specs/NativeCalculator.ts
import type { TurboModule } from 'react-native';
import { TurboModuleRegistry } from 'react-native';

export interface Spec extends TurboModule {
  add(a: number, b: number): number;
}

export default TurboModuleRegistry.getEnforcing<Spec>('NativeCalculator');

Linking Native Code

# Auto-linking (RN 0.60+)
cd ios && pod install
cd android && ./gradlew build

Performance Optimization

Enable Hermes

// android/app/build.gradle
hermesEnabled = true

// ios: Already default with New Architecture

Performance Monitoring

import { PerformanceObserver } from 'react-native-performance';

new PerformanceObserver((list) => {
  list.getEntries().forEach(entry => {
    console.log(`${entry.name}: ${entry.duration}ms`);
  });
}).observe({ entryTypes: ['measure'] });

Image Optimization

// Use FastImage for better caching
import FastImage from 'react-native-fast-image';

<FastImage
  source={{ uri: 'https://example.com/image.jpg' }}
  resizeMode={FastImage.resizeMode.cover}
/>

Device Testing

iOS Simulator

# List devices
xcrun simctl list devices

# Boot specific device
xcrun simctl boot "iPhone 16 Pro"

# Run on device
npx react-native run-ios --device "My iPhone"

Android Emulator

# List AVDs
emulator -list-avds

# Run emulator
emulator -avd Pixel_8_API_35

# Run on device
npx react-native run-android --deviceId <device-id>

Debugging

Flipper (Deprecated)

# Use Chrome DevTools instead (RN 0.73+)
# Press 'j' in Metro to open debugger

React DevTools

npx react-devtools

Common Debug Patterns

// Native crash on iOS
// Check: Xcode → Device and Simulators → View Device Logs

// Bridge error
// Clear Metro cache and rebuild
watchman watch-del-all
npx react-native start --reset-cache

// Android build failure
cd android && ./gradlew clean && cd ..

Environment Variables

# ~/.zshrc or ~/.bash_profile
export ANDROID_HOME=$HOME/Library/Android/sdk
export PATH=$PATH:$ANDROID_HOME/emulator
export PATH=$PATH:$ANDROID_HOME/platform-tools
export PATH=$PATH:$ANDROID_HOME/cmdline-tools/latest/bin

# Reload
source ~/.zshrc

Health Check

node --version      # 20+
xcodebuild -version # 16.1+
pod --version       # 1.15+
adb --version
watchman version
eas --version       # Expo

Related Skills

• mobile-architect - Architecture decisions