If you've been working with React Native or following its evolution, you've probably heard about the "New Architecture." But what exactly changed, and why does it matter? Let's break down the fundamental differences between React Native's old bridge system and the new architecture that's revolutionizing mobile development.
When React Native first launched, it introduced a clever solution to run JavaScript code alongside native iOS and Android code. At its core was the "bridge" - a communication layer that allowed JavaScript and native code to talk to each other.
Imagine you're building a React Native app. Your code lives in three main spaces:
JavaScript Thread: This is where your React components, business logic, and state management run. When React determines the UI needs updating, it calculates changes in its Virtual DOM here.
The Bridge: Think of this as a messenger service. When JavaScript needed to update the UI or call a native feature (like the camera), it would:
Native UI Thread: This is where your actual native components (like iOS's UIView or Android's TextView) get rendered and displayed on screen.
Here's what a typical interaction looked like:
// JavaScript side
const updateButtonColor = (color) => {
// This gets serialized to JSON and sent across the bridge
NativeModules.UIManager.updateView(buttonId, {
backgroundColor: color,
});
};
The data would travel: JavaScript → JSON serialization → Bridge → JSON deserialization → Native code
While this architecture worked, it had some serious limitations:
1. The Serialization Bottleneck
Every piece of data had to be converted to JSON and back. For simple operations, this wasn't a big deal. But for complex animations, rapid gestures, or large data transfers, this serialization overhead became a performance killer. Imagine trying to animate 60 frames per second while constantly converting data to JSON and back!
2. Asynchronous Communication
Since all communication was asynchronous, JavaScript couldn't directly wait for native operations to complete. This made certain operations clunky and led to "bridge traffic jams" where messages would queue up, causing UI lag and dropped frames.
3. Single JavaScript Thread
Your JavaScript thread was doing triple duty: running your app logic, managing state, AND handling all bridge communication. When the JS thread got busy with heavy computations, UI updates would get delayed, leading to that dreaded "janky" feeling.
4. Limited Type Safety
There was no automatic way to ensure that the data JavaScript sent matched what the native side expected. This led to runtime errors that could have been caught earlier.
5. Slow Startup Times
All native modules typically had to be loaded and initialized when your app started, even if you weren't using them right away. This bloated app startup times and memory usage.
The New Architecture (sometimes called the "Fabric" architecture or "JSI-based" architecture) isn't just an incremental improvement - it's a fundamental rethinking of how React Native works. The key innovation? Eliminating the bridge entirely and replacing it with direct communication between JavaScript and native code.
Let's break down the four pillars of the new system:
JSI is the foundation of everything. It's a lightweight C++ layer that allows JavaScript to directly hold references to native C++ objects and call their methods - and vice versa.
Think about what this means: Instead of serializing data to JSON, sending it across a bridge, and deserializing it, JavaScript can now directly call native functions. It's like upgrading from sending letters to having a direct phone line.
// With JSI, this is a direct synchronous call
const result = nativeModule.someFunction(arg1, arg2);
// No JSON, no bridge, just a direct C++ function call
Fabric replaces the old UI Manager and Shadow Tree system. It's a C++ rendering layer that manages UI components across both platforms.
Key improvements:
When you update your UI now, the path is: JavaScript → JSI → Fabric (C++) → Native UI - all synchronously!
TurboModules are the new generation of Native Modules, built on top of JSI. They bring three major improvements:
Direct Synchronous Calls: No more asynchronous bridge crossing. If you need the battery level, you get it immediately.
// Old way - asynchronous
NativeModules.BatteryModule.getBatteryLevel().then((level) =>
console.log(level)
);
// New way - synchronous with TurboModules
const level = TurboModuleRegistry.get("BatteryModule").getBatteryLevel();
console.log(level);
Lazy Loading: Modules are only loaded when you actually use them. This dramatically improves app startup time and reduces memory usage.
Type Safety: TurboModules work with Codegen to ensure type consistency between JavaScript and native code.
Codegen is a build-time tool that automatically generates interface code for both JavaScript and native platforms. It reads your component or module definitions and creates:
This ensures that your JavaScript code and native code always agree on data types and function signatures, catching errors at build time rather than runtime.
| Aspect | Old Bridge | New Architecture |
|---|---|---|
| Communication | Asynchronous JSON messages | Synchronous C++ function calls via JSI |
| Performance | Serialization overhead, bridge bottlenecks | Direct calls, minimal overhead |
| Native Modules | Eager loading, async calls | Lazy loaded TurboModules, sync calls |
| UI Rendering | Async UI Manager + Yoga | Synchronous Fabric renderer |
| Type Safety | Manual, error-prone | Auto-generated with Codegen |
| Concurrency | Limited | Full React Concurrent Mode support |
| Debugging | Complex across async boundaries | Easier with synchronous calls |
So what does all this technical jargon actually mean for your app?
The New Architecture aligns React Native more closely with React's core principles and with native development practices. This means:
You might wonder why it's called the "Fiber" architecture. React Fiber is React's reconciliation algorithm that allows for interruptible rendering and work prioritization. The New Architecture in React Native is specifically designed to fully leverage these Fiber capabilities.
Fabric (the rendering engine) works hand-in-hand with React Fiber to translate React's rendering output into native UI commands efficiently. So while the technical components are JSI, Fabric, TurboModules, and Codegen, they all work together to support and enhance what React Fiber brings to the table.
If you're working on a new React Native project, the New Architecture is the way to go. For existing apps, the migration might require some work, especially if you have custom native modules, but the performance and developer experience improvements make it worthwhile.
The React Native team has put significant effort into making the migration path as smooth as possible, with extensive documentation and tools to help you through the process.
The shift from the old bridge to the New Architecture represents one of the most significant improvements in React Native's history. By replacing asynchronous message passing with direct synchronous communication, React Native has addressed its fundamental performance limitations while maintaining the developer-friendly experience that made it popular in the first place.
The result? Apps that feel faster, more responsive, and more "native" - all while keeping the productivity benefits of React development. That's a win for everyone.
Have questions about migrating to the New Architecture or implementing TurboModules? Feel free to reach out - I'd love to hear about your experiences!