React Native Architecture Migration Guide
React Native architecture has undergone a fundamental transformation with the New Architecture featuring Fabric, TurboModules, and JSI. Therefore, understanding these components is essential for teams maintaining or building production mobile applications. As a result, this guide provides a complete walkthrough of the migration process with practical implementation patterns.
Understanding the New Architecture Components
The New Architecture replaces the asynchronous bridge with JavaScript Interface (JSI) for direct native module communication. Moreover, Fabric is the new rendering system that enables synchronous layout calculations and concurrent rendering features. Specifically, JSI allows JavaScript to hold references to C++ host objects, eliminating the JSON serialization overhead of the old bridge.
TurboModules replace the legacy native module system with lazy-loaded, type-safe modules. Furthermore, codegen generates native interface code from JavaScript type definitions, ensuring type consistency between JavaScript and native layers. Consequently, runtime errors from type mismatches decrease significantly in production applications.
New Architecture components: JSI, Fabric, and TurboModules
TurboModule Spec Definition
TurboModules start with a TypeScript specification that codegen transforms into native C++ interfaces. Additionally, the spec defines method signatures, return types, and synchronous vs asynchronous behavior. In contrast to legacy native modules that loaded eagerly at startup, TurboModules initialize on first access.
// NativeDeviceInfo.js — TurboModule Spec
import type { TurboModule } from 'react-native';
import { TurboModuleRegistry } from 'react-native';
export interface Spec extends TurboModule {
// Synchronous methods (executed on JS thread via JSI)
getDeviceModel(): string;
getBatteryLevel(): number;
getStorageInfo(): {
total: number;
available: number;
used: number;
};
// Asynchronous methods
getNetworkStatus(): Promise<{
type: string;
isConnected: boolean;
strength: number;
}>;
// Event emitter support
addListener(eventName: string): void;
removeListeners(count: number): void;
}
export default (TurboModuleRegistry.getEnforcing<Spec>(
'DeviceInfo'
): Spec);
// C++ Native implementation (DeviceInfoModule.h)
// #pragma once
// #include <NativeDeviceInfoSpec.h>
//
// class DeviceInfoModule : public NativeDeviceInfoCxxSpec {
// public:
// DeviceInfoModule(std::shared_ptr<CallInvoker> jsInvoker);
// jsi::String getDeviceModel(jsi::Runtime& rt);
// double getBatteryLevel(jsi::Runtime& rt);
// jsi::Object getStorageInfo(jsi::Runtime& rt);
// AsyncPromise<jsi::Object> getNetworkStatus(jsi::Runtime& rt);
// };
This specification drives code generation for both platforms. Therefore, native implementations must conform to the exact interface defined in the spec file.
Fabric Renderer and Concurrent Features
Fabric renders UI synchronously on the JavaScript thread when needed, enabling features like synchronous measure and layout. For example, this eliminates the layout thrashing that caused visual jumps in the old architecture when navigating between screens. However, custom native components require migration to the new Fabric component protocol.
Concurrent rendering support allows React Native to interrupt and resume rendering work. Moreover, Suspense and transitions work correctly with Fabric, enabling smooth UI updates even during expensive re-renders. As a result, scroll performance and gesture responsiveness improve measurably in complex applications.
Fabric renderer enabling synchronous layout and concurrent features
React Native Architecture Migration Strategy
The interop layer allows old and new architecture components to coexist during migration. Additionally, React Native provides migration guides and compatibility flags to enable gradual adoption. Meanwhile, popular libraries like React Navigation and Reanimated have already shipped New Architecture support, reducing the migration burden for most applications.
Start migration by enabling the New Architecture flag in your Gradle and Podfile configuration. Furthermore, test thoroughly with your existing native modules to identify compatibility issues early. Consequently, teams that follow an incremental migration approach avoid the risks of a complete rewrite while gaining performance benefits progressively.
Incremental migration testing from old to new architecture
Related Reading:
Further Resources:
In conclusion, the React Native architecture migration delivers substantial performance improvements through JSI, Fabric, and TurboModules. Therefore, plan your migration incrementally using the interop layer and prioritize TurboModule conversion for native modules that impact startup time and user interaction responsiveness.