React Native architecture (bridge, new architecture)

Introduction

React Native lets you build mobile apps using JavaScript. It uses a special system to connect your JavaScript code with native mobile parts so your app feels fast and smooth.

When you want to build a mobile app using JavaScript but still use native phone features.

When you want your app to work on both iPhone and Android with mostly the same code.

When you want to improve app speed by using the new React Native system.

When you want to understand how React Native talks to native phone parts.

When you want to debug or optimize your React Native app's performance.

Syntax

React Native

/* React Native uses a Bridge to connect JavaScript and native code */
// Old architecture:
JavaScript thread <--> Bridge <--> Native thread

// New architecture (Fabric + TurboModules):
JavaScript thread <--> JS Interface <--> Native Modules + Fabric Renderer

The Bridge is like a messenger between JavaScript and native code.

The New Architecture improves speed by reducing the bridge and using direct calls.

Examples

This sends a message over the bridge to the native side to show an alert.

React Native

// Old Bridge example
// JS sends a command to native to show an alert
NativeModules.AlertManager.showAlert('Hello!')

This calls the native module faster using the new system.

React Native

// New Architecture uses TurboModules
// JS calls native module directly without bridge delay
const alertModule = require('AlertModule');
alertModule.showAlert('Hello!')

Sample App

This simple app shows a button. When you press it, it uses React Native's native alert feature. Behind the scenes, React Native uses its architecture to connect the JavaScript button press to the native alert popup.

React Native

import React from 'react';
import {Button, Alert, View} from 'react-native';

export default function App() {
  const showAlert = () => {
    Alert.alert('Hello from React Native!');
  };

  return (
    <View style={{flex: 1, justifyContent: 'center', alignItems: 'center'}}>
      <Button title="Press me" onPress={showAlert} accessibilityLabel="Show alert button" />
    </View>
  );
}

Important Notes

The old bridge sends messages back and forth, which can slow down complex apps.

The new architecture uses Fabric for UI and TurboModules for faster native calls.

Understanding this helps you write better React Native apps and debug performance issues.

Summary

React Native connects JavaScript and native code using a bridge system.

The new architecture improves speed by reducing bridge overhead.

Knowing this helps you build faster and smoother mobile apps.

Practice

1. What is the main role of the bridge in React Native architecture?

easy

A. It manages the app's navigation stack.

B. It compiles JavaScript into native machine code.

C. It connects JavaScript code with native platform code.

D. It handles styling and layout of components.

Solution

1. Step 1: Understand the bridge concept

   The bridge acts as a communication layer between JavaScript and native code in React Native.

2. Step 2: Identify the bridge's role

   It allows JavaScript to send commands and receive data from native modules, enabling cross-platform functionality.

3. Final Answer:

   It connects JavaScript code with native platform code. -> Option C

4. Quick Check:

   Bridge = Connect JS and native [OK]

Hint: Bridge links JS and native code in React Native [OK]

Common Mistakes:

• Thinking bridge compiles JavaScript
• Confusing bridge with navigation or styling
• Assuming bridge handles UI rendering directly

2. Which of the following is the correct way to describe the new React Native architecture?

easy

A. It removes the need for native code entirely.

B. It replaces JavaScript with a new language.

C. It uses a webview to render all components.

D. It improves performance by reducing bridge overhead.

Solution

1. Step 1: Recall the new architecture goal

   The new React Native architecture aims to make apps faster by optimizing communication.

2. Step 2: Understand how it improves performance

   It reduces the overhead caused by the bridge, making interactions between JS and native code more efficient.

3. Final Answer:

   It improves performance by reducing bridge overhead. -> Option D

4. Quick Check:

   New architecture = less bridge overhead [OK]

Hint: New architecture reduces bridge overhead for speed [OK]

Common Mistakes:

• Believing it removes native code completely
• Thinking it replaces JavaScript language
• Confusing it with webview-based rendering

3. Given the following code snippet, what will happen when the JavaScript calls NativeModules.ExampleModule.getData() in React Native's old architecture?

medium

A. The call is sent over the bridge asynchronously.

B. The call goes directly to native code without delay.

C. The call causes a syntax error in JavaScript.

D. The call is handled by a webview component.

Solution

1. Step 1: Understand NativeModules call behavior

   In old React Native, calls to native modules go through the bridge asynchronously.

2. Step 2: Identify the effect of the bridge

   The bridge queues and sends messages between JS and native code, causing asynchronous behavior.

3. Final Answer:

   The call is sent over the bridge asynchronously. -> Option A

4. Quick Check:

   Old architecture calls = async bridge [OK]

Hint: Old architecture uses async bridge calls [OK]

Common Mistakes:

• Assuming direct synchronous native calls
• Thinking it causes syntax errors
• Confusing with webview handling

4. You notice your React Native app is slow due to many bridge calls. Which change can help fix this performance issue?

medium

A. Rewrite all JavaScript code in TypeScript.

B. Switch to the new architecture with TurboModules and Fabric.

C. Remove all native modules and use only JavaScript.

D. Use a webview to render the entire app.

Solution

1. Step 1: Identify cause of slowness

   Many bridge calls cause overhead and slow down the app.

2. Step 2: Choose the right fix

   The new architecture uses TurboModules and Fabric to reduce bridge overhead and improve speed.

3. Final Answer:

   Switch to the new architecture with TurboModules and Fabric. -> Option B

4. Quick Check:

   New architecture reduces bridge calls [OK]

Hint: Use new architecture to reduce bridge calls [OK]

Common Mistakes:

• Thinking TypeScript improves bridge performance
• Removing native modules breaks functionality
• Using webview slows app further

5. How does the new React Native architecture improve UI rendering performance compared to the old bridge system?

hard

A. By using Fabric to directly manage UI components on the native side.

B. By compiling JavaScript into native code at build time.

C. By removing the need for any native code in the app.

D. By rendering UI inside a webview for faster updates.

Solution

1. Step 1: Understand Fabric's role

   Fabric is the new rendering system that manages UI components natively.

2. Step 2: Compare with old bridge system

   Old system sent UI updates over the bridge causing delays; Fabric reduces this by direct native management.

3. Final Answer:

   By using Fabric to directly manage UI components on the native side. -> Option A

4. Quick Check:

   Fabric improves UI by native management [OK]

Hint: Fabric manages UI natively for speed [OK]

Common Mistakes:

• Thinking JavaScript is compiled to native code
• Believing native code is removed
• Confusing Fabric with webview rendering