Migrating a Large App to the New React Native Architecture

The New React Native Architecture which combines Fabric with TurboModules and JSI will deliver improved application startup times and better animation performance and enhanced reliability of the connection between native code and JavaScript code.

The process of migrating a complete production application requires more effort than simply using a switch to complete the task.

In this post, I will present a complete guide which includes:

• The actual architectural differences which exist in the new system
• The complete process for migrating large applications
• The most frequent mistakes
• Code examples (JS + Native)
• The effects of this situation on react native app development services and the total development expenses for react native applications

Why the New Architecture Matters

The legacy React Native bridge used asynchronous JSON serialization for its data processing which resulted in the following problems:

• Frame drops
• Expensive re-renders
• Complex native module code

The new architecture introduces:

• JavaScript Interface (JSI) which enables synchronous access to native methods
• TurboModules which provide faster access to typed native modules
• Fabric which functions as a modern renderer that operates concurrently and matches the specifications of React 18.

For large apps, this means:

• The system provides improved performance for large applications.
• The system enables developers to create more maintainable native code.
• The system allows developers to implement upgrades throughout the entire application lifecycle.

Migration Strategy for Large Apps

Do not migrate everything at once

Phase 1: Preparation

Before enabling anything:
npx react-native doctor

Checklist:

• React Native ≥ 0.70
• Remove deprecated libraries
• Update all native dependencies
• Enable Hermes (mandatory for new architecture)

// android/app/build.gradle
enableHermes: true

Phase 2: Enable the New Architecture (Safely)

Enable it per-platform first.

Android

android/gradle.properties

newArchEnabled=true

iOS

ios/Podfile

ENV['RCT_NEW_ARCH_ENABLED'] = '1'
Then install pods:

cd ios && pod install
Expect build errors at this stage, that’s normal.

Migrating Native Modules to TurboModules

Legacy Native Module (Android):
@ReactModule(name = CounterModule.NAME)
public class CounterModule extends ReactContextBaseJavaModule {
public static final String NAME = "Counter";

@override
public String getName() {
return NAME;
}

@ReactMethod
public void increment(Promise promise) {
promise.resolve(1);
}
}
TurboModule Version (Android)

1. Define the spec (TypeScript)
// NativeCounter.ts
import type { TurboModule } from 'react-native';
import { TurboModuleRegistry } from 'react-native';

export interface Spec extends TurboModule {
increment(): number;
}

export default TurboModuleRegistry.getEnforcing(
'Counter'
);

2. Implement in Java
public class CounterModule extends NativeCounterSpec {
@override
public double increment() {
return 1;
}
}

Benefits:

• Type safety
• No async bridge
• Faster calls

Fabric: Migrating Custom UI Components

Fabric replaces UIManager with C++ shadow nodes.

Old View Manager
public class MyViewManager extends SimpleViewManager {
@override
public String getName() {
return "MyView";
}
}

Fabric Component (High-Level)

• Define props in TypeScript
• Generate code via Codegen
• Implement native renderer

Fabric migration is the most complex part, so prioritize:

• High-traffic components
• Animation-heavy views
• Scrolling lists

Handling Third-Party Libraries

This is where most migrations fail.

What to Do

Audit dependencies:

npm ls react-native

Check support:

TurboModules?
Fabric?
Maintained?

Common Fix

Temporarily disable unsupported libraries using interop mode while waiting for updates.

How Migration Affects React Native App Development Cost

Short-Term

• Higher engineering cost
• Native expertise required
• Build pipeline changes

Long-Term

• Faster feature development
• Lower maintenance
• Fewer performance hotfixes

The react native app development cost for enterprise apps decreases during the first 12 to 18 months because of better stability and improved scalability.

Key Lessons Learned

• Migrate incrementally
• Start with TurboModules, then Fabric
• Expect native build issues
• Invest in automated testing
• Document everything

Final Thoughts

The New React Native Architecture functions as a mandatory requirement for developers since it represents the upcoming direction of the ecosystem. Your organization should start migration now because it will provide multiple benefits. The migration process will help your organization reduce technical debt while it will also bring performance improvements and create a protective measure against future system issues. The migration process will provide your organization with better technical knowledge and cost-effective solutions whether your selected React Native app development company develops applications internally or assesses react native app development services.