Expo App Config Generator

app.json is the static configuration file for Expo projects. It defines your app's name, version, icons, splash screen, permissions, and platform-specific settings. app.config.js is the dynamic version — it's a JavaScript file that exports a config object, allowing environment variables, conditional logic, and dynamic values at build time.

Use app.config.js when you need: (1) environment-specific configs (dev/staging/prod), (2) secrets from environment variables rather than checked-in files, (3) dynamic version numbers from package.json, or (4) conditional feature flags. app.json is simpler and sufficient for static projects.

Expo plugins (config plugins) are functions that modify your native app configuration during the prebuild/EAS Build process. They let packages like expo-camera, expo-notifications, and expo-location add required native code, permissions, and entitlements automatically. You list them in the 'plugins' array. Most popular packages include their own config plugin.

Camera: NSCameraUsageDescription (iOS) + android.permission.CAMERA. Location: NSLocationWhenInUseUsageDescription + android.permission.ACCESS_FINE_LOCATION. Notifications: no extra permissions needed on iOS (requested at runtime). Microphone: NSMicrophoneUsageDescription + android.permission.RECORD_AUDIO. Contacts: NSContactsUsageDescription + android.permission.READ_CONTACTS.

EAS Build is Expo's cloud build service. It reads your app.config.js at build time, applies config plugins to generate native code (android/, ios/ folders), then builds the APK/IPA. You can use process.env variables in app.config.js to inject different values per environment — set them in eas.json or as EAS secrets. This is the recommended way to manage build-time configuration.