Expo CLI & Dev Highlights Summary

Every highlight bullet from the 8 pages in this section, gathered on one page and grouped by the page it came from.

Local Development Basics

• npx expo start launches Metro, prints a QR code, and keeps Fast Refresh running on save
• LAN is the default and fastest path when your laptop and phone share Wi‑Fi
• Tunnel reaches devices across VPNs and corporate firewalls - expect slower reloads
• Press i or a in the terminal to boot the iOS Simulator or Android emulator without retyping flags
• Expo Go is fastest for SDK-only modules; expo-dev-client is required once you add custom native code
• --clear resets Metro cache after dependency, Babel, or SDK changes
• Team package.json scripts keep host mode and client type consistent across machines

iOS Simulator & Android Emulator

• Press i or a in Expo CLI to launch iOS Simulator or Android Emulator
• Shift+I and Shift+A pick a specific device when the default is wrong
• Android 16 (API 36) SDK is required to compile RN 0.86 - install it in Android Studio
• Capture simulator screenshots with xcrun simctl and adb for visual regression baselines
• Run a device matrix across phone, tablet, and OS versions before release

Physical Device Testing

• Android: enable USB debugging, verify with adb devices, then npx expo run:android
• iOS: trust the Mac, enable Developer Mode on iOS 16+, pair in Xcode Devices window
• Wireless debugging removes the cable after the first USB pairing
• Internal distribution via EAS puts QA builds on TestFlight and Play internal tracks
• Physical hardware is mandatory for camera, push, haptics, and store-like performance

expo-dev-client

• npx expo install expo-dev-client adds the development-build launcher and dev menu
• Configure launchMode and defaultLaunchURL in app.json - requires a native rebuild
• registerDevMenuItems adds team shortcuts without forking native code
• npx expo start --dev-client serves JS to your custom binary, not Expo Go
• Native module changes need eas build or npx expo run:* - JS still hot-reloads

React Native DevTools

• Press j in Metro or choose Open DevTools from the in-app dev menu
• React Components panel is the element inspector - select on device, edit props live
• Performance and Network panels ship in RN 0.83+; Expo apps may still show Expo Network for some requests
• RN 0.86 adds light/dark emulation via the DevTools Command Palette - no device settings change
• Hermes is required - remote Chrome debugging via chrome://inspect is unsupported
• DevTools launches as a bundled desktop app on macOS; browser fallback exists behind corporate firewalls

Flipper & Alternative Debuggers

• Flipper is legacy for React Native JS debugging - RN DevTools replaced it from 0.76 onward
• Remote Chrome debugging and chrome://inspect are unsupported on Hermes stacks
• Use Xcode and Android Studio for native crashes, layout, and platform logs
• RN 0.85+ allows multiple CDP clients - DevTools and VS Code extensions can coexist
• Expo Go and dev-client both expose the same DevTools entry (j / dev menu)
• Reach for Flipper only for unmaintained native plugins - plan migration to RN DevTools

Hot Reload vs Fast Refresh

• Hot Reload is removed - Fast Refresh is the only live-reload path in RN 0.86
• Fast Refresh preserves function component state when the edited file exports only components
• Mixed exports (components + constants) force broader re-execution and often reset state
• Use // @refresh reset to force remount when tuning mount-only effects or animations
• Stale bundles after dependency changes need npx expo start --clear, not toggling reload modes
• useEffect always re-runs on Fast Refresh - design effects to tolerate occasional re-execution

Expo CLI Best Practices

• Default to LAN; use tunnel only when firewalls block Metro
• Adopt expo-dev-client before custom native modules
• Press j for React Native DevTools - not remote Chrome debugging
• Clear Metro cache when Fast Refresh behaves inconsistently
• Test on physical devices before every release candidate
• Rebuild dev client after SDK or native dependency changes

3730363230327c3732396f6967637c6f692e73656469756765646f63