Expo Brownfield

Expo Brownfield

A brownfield app is an existing native iOS or Android app that adopts React Native incrementally, as opposed to a greenfield app that is React Native from day one.

Expo supports two distinct ways to add React Native to a brownfield project:

For the full decision matrix, see ./references/comparison.md.

Pick an approach

Use these quick rules — fall through to comparison.md for anything ambiguous.

• Choose isolated if the iOS/Android team must consume RN as a regular library dependency (AAR or XCFramework), without installing Node, Yarn, or the React Native build toolchain.
• Choose isolated if RN code and native code live in separate repositories or release on independent cadences.
• Choose integrated if a single team owns both the native and RN code and is willing to add React Native + Expo to the native project's Gradle and CocoaPods setup.
• Choose integrated if you want hot reload and JS source maps to work seamlessly inside the existing native build process.

References

• ./references/brownfield-isolated.md -- Build RN as AAR/XCFramework and consume from the native app (BrownfieldActivity, ReactNativeViewController, ReactNativeView)
• ./references/brownfield-integrated.md -- Add RN and Expo directly to existing Gradle and CocoaPods builds (ReactActivity, RCTRootView, Podfile)
• ./references/comparison.md -- Decision criteria, trade-offs, and scenario mapping for choosing an approach
• ./references/troubleshooting.md -- Metro connection, build, signing, and module-resolution issues common to both approaches

More information available at https://docs.expo.dev/brownfield/overview/

Shared prerequisites

Both approaches require, in the environment that builds the React Native side:

• Node.js (LTS) — runs the Expo CLI and JavaScript code.
• Yarn — manages JavaScript dependencies.

The integrated approach additionally requires CocoaPods on iOS (sudo gem install cocoapods). The isolated approach does not require CocoaPods or any RN tooling in the consuming native app.