Understanding Continuous Native Generation (CNG) in React Native: Expo Go vs. CNG Workflows

React Native development has evolved significantly with tools like Expo, which simplify building cross-platform apps. Two key workflows dominate the ecosystem: Expo Go (for rapid prototyping) and Continuous Native Generation (CNG) (for advanced customization). This post explores their differences, use cases, and how to leverage them effectively.

What is Continuous Native Generation (CNG)?

CNG is an Expo workflow that generates native iOS/Android projects on-demand using declarative configurations (like app.json and config plugins). Instead of manually maintaining ios and android directories, CNG creates them dynamically during builds, enabling seamless upgrades and dependency management.

Key Features of CNG:

• On-Demand Native Code: Generated via expo prebuild or expo run:android/ios.
• Config Plugins: Modify native projects programmatically (e.g., adding entitlements, dependencies).
• No Manual Maintenance: Native directories are treated as build artifacts, reducing upgrade friction.

Expo Go: The Quickstart Workflow

Expo Go is a prebuilt app for testing React Native projects instantly via QR code. It’s ideal for:

• Prototyping without native code.
• Sharing demos with stakeholders.

Limitations:

• No Custom Native Code: Apps using native modules (e.g., react-native-mmkv) crash in Expo Go.
• Restricted APIs: Limited to Expo SDK features (e.g., camera, notifications).

CNG vs. Expo Go: A Side-by-Side Comparison

Workflow Examples

1. Switching from Expo Go to CNG

To add native functionality (e.g., react-native-mmkv):

1. Update package.json Scripts:
   "android": "expo run:android",
   "ios": "expo run:ios"
2. Remove Native Directories: rm -rf android ios
3. Run CNG:npx expo prebuild --clean # Generates fresh native projects
   npm run android # Builds and launches the app

2. Adding a Home Screen Widget with CNG

Using CNG’s config plugins, you can generate native iOS targets for widgets:

{  
  "plugins": [  
    ["@bacons/widgets", { "targetName": "MyWidget" }]  
  ]  
}  

When to Use Each Workflow

• Expo Go:
  • Early-stage prototyping.
  • Apps without custom native code.
  • Teams needing rapid iteration.
• CNG:
  • Apps requiring native modules (e.g., Bluetooth, custom SDKs).
  • Projects needing platform-specific configurations (e.g., App Groups for widgets) 10.
  • Long-term maintainability with automated native code generation.

Conclusion

Expo Go and CNG cater to different stages of app development. While Expo Go accelerates initial prototyping, CNG empowers developers to scale apps with native features without sacrificing Expo’s tooling. By understanding their strengths, teams can choose the right workflow for their project’s lifecycle.

Further Reading:

• Expo’s Official CNG Documentation 
• Building Apple Widgets with CNG 

Visual Appendix

Diagram: Expo Go vs. CNG Workflow

Expo Go Workflow:
[JS Code] → Expo Go App → Instant Preview

CNG Workflow:
[JS Code + Config Plugins] → expo prebuild → [Native Projects] → Local/EAS Build → Production App

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