Expo

Overview

Expo is a development platform for React Native that provides file-based routing (Expo Router), cloud builds (EAS Build), automated store submissions (EAS Submit), and over-the-air updates (EAS Update). It includes 50+ SDK modules for native device APIs and lets developers ship iOS and Android apps without managing Xcode or Android Studio.

Instructions

• When starting a new app, use npx create-expo-app with TypeScript and set up Expo Router for file-based navigation in the app/ directory with layouts, dynamic routes, and route groups.
• When building for production, configure EAS Build profiles (development, preview, production) in eas.json and use cloud builds instead of local builds for reproducibility.
• When deploying updates, use EAS Update for instant JavaScript-only bug fixes that bypass app store review, with channel-based routing and rollback support.
• When accessing device APIs, use Expo SDK modules (expo-camera, expo-location, expo-notifications, expo-secure-store) and config plugins to handle native permissions without ejecting.
• When testing, use Expo Go for quick iteration on physical devices, and development builds for testing custom native modules.
• When optimizing performance, use expo-image over the built-in Image component for caching and modern format support, and configure splash screens and app icons via app.config.ts.

Examples

Example 1: Build a mobile app with tab navigation and push notifications

User request: "Create an Expo app with tabs, push notifications, and deep linking"

Actions:

1. Scaffold with npx create-expo-app and set up Expo Router with app/(tabs)/_layout.tsx
2. Configure expo-notifications for push notifications (APNs and FCM) with config plugin
3. Add deep linking via universal links in app.config.ts
4. Set up EAS Build profiles and EAS Submit for App Store and Google Play

Output: A tab-based mobile app with push notifications, deep linking, and automated store submission.

Example 2: Ship a bug fix via over-the-air update

User request: "Push an urgent fix to production without going through app store review"

Actions:

1. Fix the bug in the JavaScript/TypeScript code
2. Run eas update --channel production to publish the update
3. Verify the update fingerprint to ensure no native code changes are required
4. Monitor rollout and use rollback if issues are detected

Output: A production fix deployed instantly to all users without waiting for app store review.

Guidelines

• Use Expo Router for navigation since file-based routing is simpler and supports deep linking automatically.
• Use EAS Build instead of local builds for reproducible, cross-platform builds without local Xcode or Android Studio.
• Use expo-image over Image for better caching, transitions, and modern format support (WebP, AVIF).
• Store sensitive data in expo-secure-store, never in AsyncStorage or MMKV which are unencrypted.
• Use config plugins instead of ejecting to keep managed workflow benefits.
• Use development builds for testing native modules since Expo Go does not support custom native code.