Expo Framework Rule Skill

Expo SDK Features and APIs

Core Expo Modules

FileSystem:

import * as FileSystem from 'expo-file-system';

// Read file
const content = await FileSystem.readAsStringAsync(FileSystem.documentDirectory + 'file.txt');

// Download file
const download = await FileSystem.downloadAsync(
  'https://example.com/file.pdf',
  FileSystem.documentDirectory + 'file.pdf'
);

Camera:

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

function CameraScreen() {
  const [permission, requestPermission] = useCameraPermissions();

  if (!permission?.granted) {
    return <Button onPress={requestPermission} title="Grant Permission" />;
  }

  return (
    <CameraView
      style={{ flex: 1 }}
      onBarcodeScanned={({ data }) => console.log(data)}
    />
  );
}

Location:

import * as Location from 'expo-location';

const getLocation = async () => {
  const { status } = await Location.requestForegroundPermissionsAsync();

  if (status !== 'granted') {
    return;
  }

  const location = await Location.getCurrentPositionAsync({
    accuracy: Location.Accuracy.High,
  });

  return location.coords;
};

Notifications:

import * as Notifications from 'expo-notifications';

// Configure notification handler
Notifications.setNotificationHandler({
  handleNotification: async () => ({
    shouldShowAlert: true,
    shouldPlaySound: true,
    shouldSetBadge: true,
  }),
});

// Schedule notification
await Notifications.scheduleNotificationAsync({
  content: {
    title: 'Reminder',
    body: 'Time to check your app!',
  },
  trigger: { seconds: 60 },
});

Asset Management

import { Image } from 'expo-image';
import { Asset } from 'expo-asset';

// Preload assets
await Asset.loadAsync([
  require('./assets/logo.png'),
  require('./assets/background.jpg'),
]);

// Optimized image component
<Image
  source={require('./assets/photo.jpg')}
  contentFit="cover"
  transition={200}
  style={{ width: 200, height: 200 }}
/>

SQLite Database

import * as SQLite from 'expo-sqlite';

const db = await SQLite.openDatabaseAsync('mydb.db');

// Create table
await db.execAsync(`
  CREATE TABLE IF NOT EXISTS users (
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    name TEXT NOT NULL,
    email TEXT UNIQUE
  );
`);

// Insert data
await db.runAsync('INSERT INTO users (name, email) VALUES (?, ?)', 'John', 'john@example.com');

// Query data
const users = await db.getAllAsync('SELECT * FROM users');

EAS Build and Submit

eas.json Configuration

{
  "cli": {
    "version": ">= 5.0.0"
  },
  "build": {
    "development": {
      "developmentClient": true,
      "distribution": "internal",
      "channel": "development",
      "ios": {
        "simulator": true
      }
    },
    "preview": {
      "distribution": "internal",
      "channel": "preview",
      "android": {
        "buildType": "apk"
      }
    },
    "production": {
      "channel": "production",
      "autoIncrement": true,
      "env": {
        "API_URL": "https://api.production.com"
      }
    }
  },
  "submit": {
    "production": {
      "ios": {
        "ascAppId": "1234567890",
        "appleId": "user@example.com"
      },
      "android": {
        "serviceAccountKeyPath": "./google-service-account.json",
        "track": "production"
      }
    }
  }
}

Build Commands

# Development build
eas build --profile development --platform ios

# Preview build (internal testing)
eas build --profile preview --platform android

# Production build
eas build --profile production --platform all

# Build and auto-submit
eas build --profile production --auto-submit

Build Environment Variables

{
  "build": {
    "production": {
      "env": {
        "API_URL": "https://api.prod.com",
        "SENTRY_DSN": "https://..."
      }
    }
  }
}

Access in app:

const apiUrl = process.env.EXPO_PUBLIC_API_URL;

Over-the-Air (OTA) Updates

EAS Update Configuration

{
  "expo": {
    "runtimeVersion": {
      "policy": "appVersion"
    },
    "updates": {
      "url": "https://u.expo.dev/[project-id]"
    }
  }
}

Publishing Updates

# Publish to production channel
eas update --channel production --message "Fix login bug"

# Publish to preview
eas update --channel preview --message "Test new feature"

# View update history
eas update:list --channel production

Update Channels Strategy

// Different channels for different environments
production -> main branch
staging -> develop branch
preview -> feature branches

Checking for Updates in App

import * as Updates from 'expo-updates';

async function checkForUpdates() {
  if (!__DEV__) {
    const update = await Updates.checkForUpdateAsync();

    if (update.isAvailable) {
      await Updates.fetchUpdateAsync();
      await Updates.reloadAsync();
    }
  }
}

// Check on app focus
useEffect(() => {
  const subscription = AppState.addEventListener('change', state => {
    if (state === 'active') {
      checkForUpdates();
    }
  });

  return () => subscription.remove();
}, []);

Runtime Version Management

{
  "expo": {
    "runtimeVersion": "1.0.0"
  }
}

Only compatible OTA updates will be delivered to builds with matching runtime versions.

Native Module Integration

Custom Native Modules with Expo Modules API

// ios/MyModule.swift
import ExpoModulesCore

public class MyModule: Module {
  public func definition() -> ModuleDefinition {
    Name("MyModule")

    Function("hello") { (name: String) -> String in
      return "Hello \(name)!"
    }

    AsyncFunction("fetchData") { (url: String, promise: Promise) in
      // Async operation
      promise.resolve(["data": "value"])
    }
  }
}

// Usage in JavaScript
import { NativeModules } from 'react-native';

const { MyModule } = NativeModules;
const greeting = MyModule.hello('World');

Config Plugins

Create custom config plugin for native configuration:

// app-plugin.js
const { withAndroidManifest } = require('@expo/config-plugins');

const withCustomManifest = config => {
  return withAndroidManifest(config, async config => {
    const androidManifest = config.modResults;

    // Modify manifest
    androidManifest.manifest.application[0].$['android:usesCleartextTraffic'] = 'true';

    return config;
  });
};

module.exports = withCustomManifest;

Apply in app.json:

{
  "expo": {
    "plugins": ["./app-plugin.js"]
  }
}

Using Third-Party Native Libraries

Without Custom Native Code (Recommended):

npx expo install react-native-reanimated

With Custom Native Code:

npx expo install react-native-camera
npx expo prebuild

App Configuration (app.json / app.config.js)

Static Configuration (app.json)

{
  "expo": {
    "name": "My App",
    "slug": "my-app",
    "version": "1.0.0",
    "orientation": "portrait",
    "icon": "./assets/icon.png",
    "userInterfaceStyle": "automatic",
    "splash": {
      "image": "./assets/splash.png",
      "resizeMode": "contain",
      "backgroundColor": "#ffffff"
    },
    "assetBundlePatterns": ["**/*"],
    "ios": {
      "supportsTablet": true,
      "bundleIdentifier": "com.company.myapp",
      "buildNumber": "1.0.0",
      "infoPlist": {
        "NSCameraUsageDescription": "We need camera access for photos",
        "NSLocationWhenInUseUsageDescription": "Location for nearby features"
      }
    },
    "android": {
      "package": "com.company.myapp",
      "versionCode": 1,
      "adaptiveIcon": {
        "foregroundImage": "./assets/adaptive-icon.png",
        "backgroundColor": "#ffffff"
      },
      "permissions": ["CAMERA", "ACCESS_FINE_LOCATION"]
    },
    "web": {
      "favicon": "./assets/favicon.png",
      "bundler": "metro"
    },
    "plugins": [
      "expo-router",
      [
        "expo-camera",
        {
          "cameraPermission": "Allow $(PRODUCT_NAME) to access camera"
        }
      ]
    ],
    "extra": {
      "apiUrl": "https://api.example.com"
    }
  }
}

Dynamic Configuration (app.config.js)

export default ({ config }) => {
  const isProduction = process.env.APP_ENV === 'production';

  return {
    ...config,
    name: isProduction ? 'My App' : 'My App (Dev)',
    slug: 'my-app',
    extra: {
      apiUrl: isProduction ? 'https://api.production.com' : 'https://api.staging.com',
      ...config.extra,
    },
    ios: {
      ...config.ios,
      bundleIdentifier: isProduction ? 'com.company.myapp' : 'com.company.myapp.dev',
    },
    android: {
      ...config.android,
      package: isProduction ? 'com.company.myapp' : 'com.company.myapp.dev',
    },
  };
};

Environment-Specific Configuration

// app.config.js
const getEnvironment = () => {
  if (process.env.APP_ENV === 'production') {
    return {
      apiUrl: 'https://api.prod.com',
      sentryDsn: 'https://prod-sentry-dsn',
    };
  }

  return {
    apiUrl: 'https://api.dev.com',
    sentryDsn: 'https://dev-sentry-dsn',
  };
};

export default {
  expo: {
    extra: getEnvironment(),
  },
};

Access in app:

import Constants from 'expo-constants';

const apiUrl = Constants.expoConfig?.extra?.apiUrl;

Best Practices

Performance Optimization

• Use expo-image instead of React Native Image for better performance
• Enable Hermes for Android: "jsEngine": "hermes"
• Use react-native-reanimated for smooth animations
• Lazy load screens with React.lazy()

Code Splitting

import { lazy, Suspense } from 'react';

const ProfileScreen = lazy(() => import('./screens/Profile'));

function App() {
  return (
    <Suspense fallback={<LoadingScreen />}>
      <ProfileScreen />
    </Suspense>
  );
}

Error Boundaries

import * as Sentry from '@sentry/react-native';

Sentry.init({
  dsn: 'your-sentry-dsn',
  environment: __DEV__ ? 'development' : 'production',
});

export default Sentry.wrap(App);

Expo Doctor

Run before building:

npx expo-doctor

This checks for common issues with dependencies and configuration.

Memory Protocol (MANDATORY)

Before starting:

cat .claude/context/memory/learnings.md

After completing: Record any new patterns or exceptions discovered.

ASSUME INTERRUPTION: Your context may reset. If it’s not in memory, it didn’t happen.