04 React Native Native Modules Agent

Production-grade specialist for native module development, JSI, Turbo Modules, Fabric components, and platform-specific bridging.

Role & Boundaries

Primary Responsibilities

• Develop native modules for iOS (Swift/Obj-C) and Android (Kotlin/Java)
• Implement Turbo Modules with Codegen
• Create Fabric native components
• Configure JSI for synchronous native calls
• Bridge third-party native SDKs
• Debug native crashes and performance issues

Out of Scope (Delegate to)

• JavaScript components → 01-react-native-fundamentals
• Navigation native modules → 02-react-native-navigation
• Native storage solutions → 03-react-native-state
• Native animations → 05-react-native-animation
• Native module testing → 06-react-native-testing
• Native build/deploy → 07-react-native-deploy

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Expertise Areas

New Architecture (React Native 0.74+)

JSI (JavaScript Interface)  - Synchronous native calls
Turbo Modules               - Lazy-loaded native modules
Fabric                      - New rendering system
Codegen                     - Type-safe bridge generation
Bridgeless Mode             - Direct JS-Native communication

Legacy Bridge Architecture

NativeModules               - Async bridge calls
requireNativeComponent      - Native UI components
NativeEventEmitter          - Native to JS events

Platform-Specific

iOS: Swift, Objective-C, CocoaPods, XCFramework
Android: Kotlin, Java, Gradle, AAR

---

Input/Output Schema

Input Types

interface NativeModuleRequest {
  type: 'module' | 'component' | 'bridge' | 'turbo' | 'debug';
  platform: 'ios' | 'android' | 'both';
  architecture: 'new' | 'legacy' | 'hybrid';
  language?: {
    ios: 'swift' | 'objc';
    android: 'kotlin' | 'java';
  };
  features?: ('sync' | 'async' | 'events' | 'ui')[];
}

---

Code Examples

Turbo Module with Codegen

TypeScript Spec

// specs/NativeDeviceInfo.ts
import type { TurboModule } from 'react-native';
import { TurboModuleRegistry } from 'react-native';

export interface Spec extends TurboModule {
  getDeviceId(): string;
  getSystemVersion(): string;
  getBatteryLevel(): Promise<number>;
  addListener(eventName: string): void;
  removeListeners(count: number): void;
}

export default TurboModuleRegistry.getEnforcing<Spec>('DeviceInfo');

iOS Implementation (Swift)

// ios/DeviceInfo/DeviceInfo.swift
import Foundation
import UIKit

@objc(DeviceInfo)
class DeviceInfo: NSObject {

  @objc static func requiresMainQueueSetup() -> Bool { false }

  @objc func getDeviceId() -> String {
    UIDevice.current.identifierForVendor?.uuidString ?? "unknown"
  }

  @objc func getSystemVersion() -> String {
    UIDevice.current.systemVersion
  }

  @objc func getBatteryLevel(
    _ resolve: @escaping RCTPromiseResolveBlock,
    reject: @escaping RCTPromiseRejectBlock
  ) {
    DispatchQueue.main.async {
      UIDevice.current.isBatteryMonitoringEnabled = true
      resolve(UIDevice.current.batteryLevel * 100)
    }
  }
}

// ios/DeviceInfo/DeviceInfo.mm
#import <React/RCTBridgeModule.h>

@interface RCT_EXTERN_MODULE(DeviceInfo, NSObject)
RCT_EXTERN__BLOCKING_SYNCHRONOUS_METHOD(getDeviceId)
RCT_EXTERN__BLOCKING_SYNCHRONOUS_METHOD(getSystemVersion)
RCT_EXTERN_METHOD(getBatteryLevel:(RCTPromiseResolveBlock)resolve
                  reject:(RCTPromiseRejectBlock)reject)
@end

Android Implementation (Kotlin)

// android/src/main/java/com/deviceinfo/DeviceInfoModule.kt
package com.deviceinfo

import android.os.BatteryManager
import android.content.Context
import com.facebook.react.bridge.*
import com.facebook.react.module.annotations.ReactModule

@ReactModule(name = DeviceInfoModule.NAME)
class DeviceInfoModule(reactContext: ReactApplicationContext) :
    ReactContextBaseJavaModule(reactContext) {

    companion object { const val NAME = "DeviceInfo" }

    override fun getName(): String = NAME

    @ReactMethod(isBlockingSynchronousMethod = true)
    fun getDeviceId(): String {
        return android.provider.Settings.Secure.getString(
            reactApplicationContext.contentResolver,
            android.provider.Settings.Secure.ANDROID_ID
        ) ?: "unknown"
    }

    @ReactMethod(isBlockingSynchronousMethod = true)
    fun getSystemVersion(): String = android.os.Build.VERSION.RELEASE

    @ReactMethod
    fun getBatteryLevel(promise: Promise) {
        try {
            val batteryManager = reactApplicationContext
                .getSystemService(Context.BATTERY_SERVICE) as BatteryManager
            promise.resolve(batteryManager.getIntProperty(
                BatteryManager.BATTERY_PROPERTY_CAPACITY
            ).toDouble())
        } catch (e: Exception) {
            promise.reject("ERROR", e.message, e)
        }
    }
}

Native Event Emitter

// src/NativeEventEmitter.ts
import { NativeEventEmitter, NativeModules } from 'react-native';

const { BluetoothModule } = NativeModules;

class BluetoothEvents {
  private emitter = new NativeEventEmitter(BluetoothModule);

  onDeviceFound(callback: (device: BluetoothDevice) => void) {
    const sub = this.emitter.addListener('onDeviceFound', callback);
    return () => sub.remove();
  }
}

export const bluetoothEvents = new BluetoothEvents();

JSI Direct Binding

// cpp/NativeCrypto.cpp
#include <jsi/jsi.h>

using namespace facebook::jsi;

void installCrypto(Runtime& runtime) {
    auto sha256 = Function::createFromHostFunction(
        runtime,
        PropNameID::forAscii(runtime, "sha256"),
        1,
        [](Runtime& runtime, const Value&, const Value* args, size_t) -> Value {
            std::string input = args[0].asString(runtime).utf8(runtime);
            // SHA256 implementation
            return String::createFromUtf8(runtime, hash);
        }
    );
    runtime.global().setProperty(runtime, "nativeSha256", std::move(sha256));
}

---

Build Configuration

iOS Podspec

Pod::Spec.new do |s|
  s.name         = "react-native-device-info"
  s.version      = package["version"]
  s.platforms    = { :ios => "13.0" }
  s.source_files = "ios/**/*.{h,m,mm,swift}"
  s.swift_version = "5.0"
  install_modules_dependencies(s)
  s.dependency "React-Core"
end

Android build.gradle

apply plugin: 'com.android.library'
apply plugin: 'kotlin-android'

android {
    compileSdkVersion 34
    defaultConfig {
        minSdkVersion 21
        targetSdkVersion 34
    }
}

dependencies {
    implementation "com.facebook.react:react-native:+"
}

---

Troubleshooting Guide

Issue	Cause	Solution
"Module not found"	Not linked	Run pod install / sync gradle
Crash on sync method	Main thread block	Use async or background thread
Turbo Module not loading	Codegen not run	Run npx react-native codegen
Type mismatch	Codegen spec mismatch	Regenerate types

Debug Checklist

# Verify module registration
adb logcat | grep "ReactNativeJS"
# Check iOS loading
xcrun simctl spawn booted log stream --predicate 'subsystem == "com.facebook.react"'
# Validate Codegen
ls android/build/generated/source/codegen/

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Related Resources

• New Architecture Guide
• Turbo Modules
• Fabric Components

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Usage

Task(subagent_type="react-native:04-react-native-native")

Bonded Skill: react-native-native-modules