Expo

Managed React Native development platform.

When to Use

• Rapid mobile prototyping
• React Native without native code
• Over-the-air updates
• Cross-platform from single codebase

Quick Start

# Create new project
npx create-expo-app my-app
cd my-app
npx expo start

import { Text, View } from "react-native";

export default function App() {
  return (
    <View style={{ flex: 1, justifyContent: "center", alignItems: "center" }}>
      <Text>Hello Expo!</Text>
    </View>
  );
}

Core Concepts

Expo Router

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

export default function Layout() {
  return (
    <Stack>
      <Stack.Screen name="index" options={{ title: "Home" }} />
      <Stack.Screen name="[id]" options={{ title: "Details" }} />
    </Stack>
  );
}

// app/index.tsx
import { Link } from "expo-router";

export default function Home() {
  return (
    <View>
      <Link href="/user/123">Go to User</Link>
    </View>
  );
}

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

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

Expo SDK

import * as ImagePicker from "expo-image-picker";
import * as Location from "expo-location";

async function pickImage() {
  const result = await ImagePicker.launchImageLibraryAsync({
    mediaTypes: ImagePicker.MediaTypeOptions.Images,
    quality: 1,
  });

  if (!result.canceled) {
    return result.assets[0].uri;
  }
}

async function getLocation() {
  const { status } = await Location.requestForegroundPermissionsAsync();
  if (status !== "granted") return null;

  return await Location.getCurrentPositionAsync({});
}

Common Patterns

EAS Build

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

# Build
eas build --platform all
eas build --profile development

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

Environment Variables

# .env
EXPO_PUBLIC_API_URL=https://api.example.com

const apiUrl = process.env.EXPO_PUBLIC_API_URL;

Best Practices

Do:

• Use Expo Router for navigation
• Leverage EAS for builds
• Use EXPOPUBLIC for env vars
• Test on real devices

Don't:

• Eject unnecessarily
• Ignore SDK versions
• Skip OTA update testing
• Use incompatible libraries

Troubleshooting

Issue	Cause	Solution
Module not found	SDK version mismatch	Check compatibility
Build failed	Native dependency	Use dev client
Metro error	Cache issue	Clear cache

References

• Expo Documentation
• Expo Router