🧠 React Native New Architecture Explained

What Was Broken, What Got Fixed, and How It Works Internally

For years, React Native apps suffered from:

• Scroll jank

• Slow native communication

• Performance unpredictability

• “Works on iOS, lags on Android”

These were not developer mistakes.

They were architecture limitations.

React Native’s New Architecture was introduced to fix these fundamental problems, not just add features.

Let’s understand this step by step, without jargon.

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🧱 The Old Architecture (What Was the Problem?)

The old React Native architecture was built around latest around 2015–2016, when:

• JSON serialization was common

• Async communication was preferred

• Mobile hardware was slower

It had three core pillars:

1️⃣ The Bridge

• JS and Native talked via an async bridge

• Messages were serialized to JSON

• Everything crossed the bridge asynchronously

2️⃣ UI Manager

• JS described the UI

• Native decided when to actually render

3️⃣ Native Modules

• JS called native code

• Results came back later (async)

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❌ Problems With the Old Architecture

Let’s see why this caused pain.

🚫 Problem 1: Slow Communication

Every call:

JS → JSON → Bridge → Native → JSON → Bridge → JS

This meant:

• Serialization cost

• Thread hopping

• Latency

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🚫 Problem 2: No Sync Access

JS could not:

• Read native values synchronously

• Get immediate results

Everything was async, even when it didn’t need to be.

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🚫 Problem 3: JS Thread Bottleneck

• Rendering logic

• Native calls

• Business logic

All competed on one JS thread.

If JS slowed down → app felt slow.

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🚫 Problem 4: UI Jank

• Layout depended on JS finishing work

• Scroll felt delayed

• Animations stuttered

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💡 The Big Idea Behind the New Architecture

Instead of:

“JS and Native live in separate worlds”

The new architecture says:

“Let them talk directly and efficiently”

This required rebuilding the foundation, not patching it.

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🆕 What Is the New Architecture Made Of?

The new architecture has three core pillars:

1️⃣ JSI (JavaScript Interface)

2️⃣ TurboModules

3️⃣ Fabric Renderer

Let’s understand each one.

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🔗 1. JSI – The Foundation

JSI allows direct communication between:

• JavaScript

• Native code (C++ / Java / Obj-C / Swift)

No bridge.
No JSON.

📌 Think of JSI as:

“JS can now call native functions like local functions”

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⚡ 2. TurboModules – Faster Native Modules

TurboModules replace old Native Modules.

Old Way

• Async only

• JSON serialization

• Bridge overhead

New Way

• Lazy loaded

• Typed

• Can be sync or async

• Direct calls via JSI

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🧠 TurboModule Flow (Simple)

1. JS calls a native method

2. JSI directly invokes native code

3. Native returns result immediately (if sync)

4. JS continues execution

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🧩 3. Fabric – The New Renderer

Fabric replaces the old UI Manager.

What Fabric Fixes

• Better scheduling

• Concurrent rendering

• More predictable UI updates

Fabric:

• Builds UI tree in JS

• Commits it efficiently to native

• Avoids unnecessary layout work

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🔄 Old vs New Communication (Side by Side)

❌ Old Architecture

JS
 ↓ JSON
Bridge
 ↓ JSON
Native

✅ New Architecture

JS ↔ JSI ↔ Native

Less hops.
Less overhead.
More control.

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📈 Performance Improvements (What Actually Got Better)

✅ Faster Native Calls

• No serialization

• No async penalty

✅ Smoother Scrolling

• Better scheduling

• Less JS blocking

✅ Faster App Startup

• Lazy module loading

• Reduced initialization cost

✅ Better Memory Usage

• Fewer intermediate objects

• Less garbage creation

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🧪 Is the New Architecture Stable?

Yes — as of today.

Support Timeline

• Introduced experimentally around RN 0.68

• Gradually stabilized

• Production-ready in RN 0.71+

• Continually improved in newer releases

📌 Today, most new RN apps can safely enable it.

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⚙️ How to Enable New Architecture

✅ Android

In gradle.properties:

newArchEnabled=true

Then rebuild the app.

---

✅ iOS

In ios/Podfile:

use_react_native!(
  :path => config[:reactNativePath],
  :new_arch_enabled => true
)

Then:

cd ios
pod install

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🧪 Writing a TurboModule (Pseudo Code)

Native Side (Android – simplified)

@ReactModule(name = DeviceModule.NAME)
public class DeviceModule extends NativeDeviceModuleSpec {

  public static final String NAME = "DeviceModule";

  @Override
  public String getDeviceName() {
    return Build.MODEL;
  }
}

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JS Side (Using TurboModule)

import { TurboModuleRegistry } from "react-native";

const DeviceModule =
  TurboModuleRegistry.get("DeviceModule");

console.log(DeviceModule.getDeviceName());

📌 Notice:

• No bridge

• No async promise required

• Direct call

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🧠 Simple Mental Model (Remember This)

Old Architecture	New Architecture
Async only	Sync + Async
JSON bridge	Direct calls
Heavy JS thread	Leaner JS thread
UI jank common	Much smoother
Hard to scale	Scales better

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⚠️ Important Reality Check

The new architecture:

• Improves performance

• Does not fix bad code

You can still:

• Block the JS thread

• Write expensive renders

• Cause jank with poor list usage

Architecture helps — discipline still matters.

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🎯 Final Takeaway

The React Native New Architecture is not a refactor.
It is a re-foundation.

By removing the bridge and introducing JSI, TurboModules, and Fabric, React Native finally behaves like a modern mobile framework, not a compatibility layer.

If you understand this architecture:

• Performance issues make sense

• Debugging becomes easier

• Optimization becomes intentional