Expo Configuration
Use this skill when configuring Expo applications using app.json, app.config.js/ts, and EAS (Expo Application Services) configuration files.
Key Concepts
app.json Configuration
Basic static configuration:
{
"expo": {
"name": "MyApp",
"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.mycompany.myapp",
"buildNumber": "1"
},
"android": {
"adaptiveIcon": {
"foregroundImage": "./assets/adaptive-icon.png",
"backgroundColor": "#ffffff"
},
"package": "com.mycompany.myapp",
"versionCode": 1
},
"web": {
"favicon": "./assets/favicon.png"
}
}
}Dynamic Configuration (app.config.js)
Use JavaScript for dynamic configuration:
export default ({ config }) => ({
...config,
name: process.env.APP_NAME || 'MyApp',
slug: 'my-app',
version: '1.0.0',
extra: {
apiUrl: process.env.API_URL,
environment: process.env.NODE_ENV,
},
ios: {
bundleIdentifier:
process.env.NODE_ENV === 'production'
? 'com.mycompany.myapp'
: 'com.mycompany.myapp.dev',
},
android: {
package:
process.env.NODE_ENV === 'production'
? 'com.mycompany.myapp'
: 'com.mycompany.myapp.dev',
},
});TypeScript Configuration
Use TypeScript for type-safe config:
// app.config.ts
import { ExpoConfig, ConfigContext } from '@expo/config';
export default ({ config }: ConfigContext): ExpoConfig => ({
...config,
name: 'MyApp',
slug: 'my-app',
version: '1.0.0',
orientation: 'portrait',
icon: './assets/icon.png',
splash: {
image: './assets/splash.png',
resizeMode: 'contain',
backgroundColor: '#ffffff',
},
plugins: [
'expo-router',
[
'expo-camera',
{
cameraPermission: 'Allow $(PRODUCT_NAME) to access your camera.',
},
],
],
extra: {
apiUrl: process.env.API_URL,
},
});Best Practices
Environment Variables
Use environment-specific configuration:
// app.config.ts
import { ExpoConfig, ConfigContext } from '@expo/config';
const IS_DEV = process.env.NODE_ENV === 'development';
const IS_PROD = process.env.NODE_ENV === 'production';
export default ({ config }: ConfigContext): ExpoConfig => ({
...config,
name: IS_PROD ? 'MyApp' : 'MyApp (Dev)',
slug: 'my-app',
extra: {
apiUrl: IS_PROD
? 'https://api.myapp.com'
: 'https://dev-api.myapp.com',
environment: process.env.NODE_ENV,
eas: {
projectId: process.env.EAS_PROJECT_ID,
},
},
ios: {
bundleIdentifier: IS_PROD
? 'com.mycompany.myapp'
: 'com.mycompany.myapp.dev',
},
android: {
package: IS_PROD
? 'com.mycompany.myapp'
: 'com.mycompany.myapp.dev',
},
});Plugin Configuration
Configure Expo plugins:
{
"expo": {
"plugins": [
"expo-router",
[
"expo-camera",
{
"cameraPermission": "Allow $(PRODUCT_NAME) to access camera"
}
],
[
"expo-location",
{
"locationAlwaysAndWhenInUsePermission": "Allow $(PRODUCT_NAME) to use your location"
}
],
[
"expo-notifications",
{
"icon": "./assets/notification-icon.png",
"color": "#ffffff"
}
]
]
}
}EAS Build Configuration
Configure EAS builds with eas.json:
{
"cli": {
"version": ">= 5.9.0"
},
"build": {
"development": {
"developmentClient": true,
"distribution": "internal",
"ios": {
"simulator": true
}
},
"preview": {
"distribution": "internal",
"ios": {
"simulator": false
},
"android": {
"buildType": "apk"
}
},
"production": {
"autoIncrement": true
}
},
"submit": {
"production": {}
}
}Access Config in Code
Access configuration at runtime:
import Constants from 'expo-constants';
export function App() {
const apiUrl = Constants.expoConfig?.extra?.apiUrl;
const environment = Constants.expoConfig?.extra?.environment;
console.log('API URL:', apiUrl);
console.log('Environment:', environment);
return <View />;
}Common Patterns
Multi-Environment Setup
// app.config.ts
import { ExpoConfig, ConfigContext } from '@expo/config';
type Environment = 'development' | 'staging' | 'production';
const ENV: Environment = (process.env.APP_ENV as Environment) || 'development';
const config: Record<Environment, { apiUrl: string; name: string }> = {
development: {
apiUrl: 'http://localhost:3000',
name: 'MyApp (Dev)',
},
staging: {
apiUrl: 'https://staging-api.myapp.com',
name: 'MyApp (Staging)',
},
production: {
apiUrl: 'https://api.myapp.com',
name: 'MyApp',
},
};
export default ({ config: baseConfig }: ConfigContext): ExpoConfig => ({
...baseConfig,
name: config[ENV].name,
slug: 'my-app',
extra: {
apiUrl: config[ENV].apiUrl,
environment: ENV,
},
});Feature Flags
// app.config.ts
export default ({ config }: ConfigContext): ExpoConfig => ({
...config,
extra: {
features: {
enableNewUI: process.env.ENABLE_NEW_UI === 'true',
enableAnalytics: process.env.ENABLE_ANALYTICS !== 'false',
enableBetaFeatures: process.env.ENABLE_BETA === 'true',
},
},
});
// In code
import Constants from 'expo-constants';
const features = Constants.expoConfig?.extra?.features;
if (features?.enableNewUI) {
// Show new UI
}Platform-Specific Assets
{
"expo": {
"ios": {
"icon": "./assets/icon-ios.png",
"splash": {
"image": "./assets/splash-ios.png"
}
},
"android": {
"adaptiveIcon": {
"foregroundImage": "./assets/adaptive-icon-android.png",
"backgroundColor": "#ffffff"
},
"splash": {
"image": "./assets/splash-android.png"
}
}
}
}Deep Linking Configuration
{
"expo": {
"scheme": "myapp",
"slug": "my-app",
"web": {
"bundler": "metro"
},
"ios": {
"associatedDomains": ["applinks:myapp.com"]
},
"android": {
"intentFilters": [
{
"action": "VIEW",
"autoVerify": true,
"data": [
{
"scheme": "https",
"host": "myapp.com",
"pathPrefix": "/app"
}
],
"category": ["BROWSABLE", "DEFAULT"]
}
]
}
}
}Version Management
// app.config.ts
import packageJson from './package.json';
export default ({ config }: ConfigContext): ExpoConfig => ({
...config,
version: packageJson.version,
ios: {
buildNumber: process.env.IOS_BUILD_NUMBER || '1',
},
android: {
versionCode: parseInt(process.env.ANDROID_VERSION_CODE || '1', 10),
},
});Anti-Patterns
Don't Hardcode Secrets
// Bad - Secrets in config
export default {
extra: {
apiKey: 'sk_live_1234567890',
apiSecret: 'secret_key_here',
},
};
// Good - Use environment variables
export default {
extra: {
apiKey: process.env.API_KEY,
// Never commit secrets
},
};Don't Use app.json for Dynamic Config
// Bad - Can't use dynamic values in app.json
{
"expo": {
"name": process.env.APP_NAME
}
}
// Good - Use app.config.js/ts
// app.config.ts
export default {
name: process.env.APP_NAME || 'MyApp',
};Don't Forget Platform-Specific Requirements
// Bad - Missing required fields
{
"expo": {
"name": "MyApp",
"slug": "my-app"
}
}
// Good - Include all required fields
{
"expo": {
"name": "MyApp",
"slug": "my-app",
"ios": {
"bundleIdentifier": "com.mycompany.myapp"
},
"android": {
"package": "com.mycompany.myapp"
}
}
}Don't Mix Config Types
// Bad - Mixing static and dynamic
// app.json
{
"expo": {
"name": "MyApp"
}
}
// app.config.js also exists - creates conflicts
// Good - Use one or the other
// Either app.json for static config
// Or app.config.js/ts for dynamic configRelated Skills
- expo-modules: Using Expo modules configured via plugins
- expo-build: Building apps with EAS Build
- expo-updates: Configuring OTA updates