Expo Development

Continuous Native Generation

• Never eject, never edit ios/ or android/ — npx expo prebuild regenerates both from app.json / app.config.ts, so hand edits vanish. Gitignore both directories. npx expo prebuild --clean when native state is suspect.
• Native config changes go through config plugins (app.plugin.js, registered in expo.plugins) applied at prebuild time. npx create-expo-module scaffolds a Swift + Kotlin module.
• Install with npx expo install, not npm install, so versions resolve against the SDK. npx expo install --fix repairs an SDK version mismatch.

EAS Build / Update

• eas.json profiles: development = developmentClient: true + distribution: internal; preview = distribution: internal + channel; production = channel + autoIncrement: true.
• Set runtimeVersion: { policy: "fingerprint" } in app.json. eas update --channel production ships JS only — a runtimeVersion mismatch forces a new binary build, and native changes can never go OTA.
• Rollback: eas update:republish --group <previous-group-id>. Diagnose failures via eas build:list then eas build:view <id>.
• Secrets belong in EAS Secrets (eas secret:create), never app.json; device-side storage via expo-secure-store.
• iOS signing failures: eas credentials. CI/CD lives in .eas/workflows/.

Expo Router

Files under app/ are routes; a _layout.tsx per directory supplies <Stack> / <Tabs> / <Drawer>. Parenthesized directories are groups and do not appear in the URL — app/(auth)/login.tsx serves /login. Read dynamic segments with useLocalSearchParams(). Deep links require scheme in app.json; myapp://user/123 then resolves to app/user/[id].tsx.

Docs: https://docs.expo.dev/