Expo

Project Setup

npx create-expo-app@latest my-app --template tabs
cd my-app && npx expo start

Expo Router (file-based routing)

app/
├── _layout.tsx          # Root layout
├── index.tsx            # / route
├── (tabs)/
│   ├── _layout.tsx      # Tab layout
│   ├── home.tsx         # /home tab
│   └── profile.tsx      # /profile tab
└── product/[id].tsx     # /product/:id

// app/_layout.tsx
import { Stack } from 'expo-router';

export default function RootLayout() {
  return (
    <Stack>
      <Stack.Screen name="(tabs)" options={{ headerShown: false }} />
      <Stack.Screen name="product/[id]" options={{ title: 'Product' }} />
    </Stack>
  );
}

// app/product/[id].tsx
import { useLocalSearchParams } from 'expo-router';

export default function ProductScreen() {
  const { id } = useLocalSearchParams<{ id: string }>();
  return <Text>Product {id}</Text>;
}

// Navigate
import { router } from 'expo-router';
router.push('/product/123');

app.json / app.config.ts

// app.config.ts (dynamic config)
import { ExpoConfig, ConfigContext } from 'expo/config';

export default ({ config }: ConfigContext): ExpoConfig => ({
  ...config,
  name: 'My App',
  slug: 'my-app',
  version: '1.0.0',
  ios: { bundleIdentifier: 'com.example.myapp' },
  android: { package: 'com.example.myapp' },
  plugins: ['expo-camera', 'expo-location'],
  extra: {
    apiUrl: process.env.API_URL ?? 'https://api.example.com',
  },
});

EAS Build & Submit

# Install EAS CLI
npm install -g eas-cli

# Configure
eas build:configure

# Build
eas build --platform ios --profile production
eas build --platform android --profile production

# Submit to stores
eas submit --platform ios
eas submit --platform android

// eas.json
{
  "build": {
    "development": { "developmentClient": true, "distribution": "internal" },
    "preview": { "distribution": "internal" },
    "production": { "autoIncrement": true }
  }
}

EAS Update (OTA)

eas update --branch production --message "Fix login bug"

import * as Updates from 'expo-updates';

async function checkForUpdates() {
  const update = await Updates.checkForUpdateAsync();
  if (update.isAvailable) {
    await Updates.fetchUpdateAsync();
    await Updates.reloadAsync();
  }
}

Common Expo SDK Modules

// Camera
import { CameraView, useCameraPermissions } from 'expo-camera';

// Location
import * as Location from 'expo-location';
const { status } = await Location.requestForegroundPermissionsAsync();
const location = await Location.getCurrentPositionAsync({});

// Secure Store
import * as SecureStore from 'expo-secure-store';
await SecureStore.setItemAsync('token', value);
const token = await SecureStore.getItemAsync('token');

// Notifications
import * as Notifications from 'expo-notifications';
const { status } = await Notifications.requestPermissionsAsync();
const token = (await Notifications.getExpoPushTokenAsync()).data;

Anti-Patterns

| Anti-Pattern | Fix | |--------------|-----| | Ejecting for simple native needs | Use config plugins or Expo Modules API | | Hardcoded API URLs | Use app.config.ts with extra and env vars | | No EAS Update for JS fixes | Set up EAS Update for OTA patches | | Using Expo Go for production testing | Use development builds (npx expo run:ios) | | Ignoring permission UX | Request permissions contextually with explanation |

Production Checklist

• [ ] EAS Build profiles configured (dev, preview, production)
• [ ] EAS Update configured for OTA
• [ ] App store metadata and screenshots prepared
• [ ] Splash screen and app icon configured
• [ ] Environment variables via app.config.ts
• [ ] Error tracking (Sentry Expo)
• [ ] Deep linking scheme configured