Running the App

Overview

Learn how to run and test your app on different platforms during development.

Quick Start

Start Development Server

npm start

This opens Expo DevTools with options to run on different platforms.

Running on Specific Platforms

iOS Simulator (Mac Only)

npm run ios

Requirements:

• macOS computer
• Xcode installed
• iOS Simulator set up

Android Emulator

npm run android

Requirements:

• Android Studio installed
• Android Emulator configured
• At least one virtual device created

Web Browser

npm run web

Opens the app in your default browser.

Physical Device

1. Install Expo Go app on your phone

   • iOS App Store
   • Google Play Store

2. Start the development server:

   npm start

3. Scan the QR code with:

   • iOS: Camera app
   • Android: Expo Go app

Development Commands

Clear Cache and Start

npm start -- --clear

Start with Specific Port

npm start -- --port 8082

Start in Tunnel Mode (for remote testing)

npm start -- --tunnel

Hot Reload

The app automatically reloads when you save changes:

• Hot Reload: Updates without losing state
• Full Reload: Shake device or press r in terminal

Debugging

Open Developer Menu

• iOS Simulator: Cmd + D
• Android Emulator: Cmd + M (Mac) or Ctrl + M (Windows)
• Physical Device: Shake the device

Developer Menu Options

• Reload: Refresh the app
• Debug Remote JS: Open Chrome DevTools
• Toggle Inspector: Inspect UI elements
• Show Perf Monitor: View performance metrics

Console Logs

View logs in the terminal where you ran npm start.

console.log('Debug message');
console.warn('Warning message');
console.error('Error message');

Platform-Specific Testing

iOS Testing Checklist

• [ ] Test on different iPhone sizes
• [ ] Test landscape orientation
• [ ] Test dark mode
• [ ] Test with VoiceOver (accessibility)
• [ ] Test push notifications

Android Testing Checklist

• [ ] Test on different screen sizes
• [ ] Test landscape orientation
• [ ] Test dark mode
• [ ] Test with TalkBack (accessibility)
• [ ] Test back button behavior

Common Issues

"Could not find a development server"

# Kill existing processes
npm start -- --clear

"Metro bundler took too long"

# Clear cache and restart
rm -rf node_modules/.cache
npm start -- --clear

"Module not found"

rm -rf node_modules
npm install
npm start -- --clear

Port Already in Use

# Use a different port
npm start -- --port 8082

iOS Simulator Not Opening

# Reset simulator
xcrun simctl shutdown all
npm run ios

Android Emulator Not Starting

1. Open Android Studio
2. Go to Device Manager
3. Start an emulator manually
4. Then run npm run android

Performance Tips

1. Use Release Mode for Performance Testing

   npx expo start --no-dev

2. Enable Hermes (enabled by default in Expo SDK 54+)

3. Profile the App

   • Open Developer Menu
   • Select "Show Perf Monitor"

Need Help?

• Check the Troubleshooting Guide
• Read the Development Guide
• Contact support for assistance