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Native Modules

Your React Native application code may need to interact with native platform APIs that aren't provided by React Native or an existing library. You can write the integration code yourself using a Turbo Native Module. This guide will show you how to write one.

The basic steps are:

  1. define a typed JavaScript specification using one of the most popular JavaScript type annotation languages: Flow or TypeScript;
  2. configure your dependency management system to run Codegen, which converts the specification into native language interfaces;
  3. write your application code using your specification; and
  4. write your native platform code using the generated interfaces to write and hook your native code into the React Native runtime environment.

Lets work through each of these steps by building an example Turbo Native Module. The rest of this guide assume that you have created your application running the command:

npx @react-native-community/cli@latest init TurboModuleExample --version 0.76.0

Native Persistent Storage​

This guide will show you how to write an implementation of the Web Storage API: localStorage. The API is relatable to a React developer who might be writing application code on your project.

To make this work on mobile, we need to use Android and iOS APIs:

1. Declare Typed Specification​

React Native provides a tool called Codegen, which takes a specification written in TypeScript or Flow and generates platform specific code for Android and iOS. The specification declares the methods and data types that will pass back and forth between your native code and the React Native JavaScript runtime. A Turbo Native Module is both your specification, the native code you write, and the Codegen interfaces generated from your specification.

To create a specs file:

  1. Inside the root folder of your app, create a new folder called specs.
  2. Create a new file called NativeLocalStorage.ts.
info

You can see all of the types you can use in your specification and the native types that are generated in the Appendix documentation.

Here is an implementation of the localStorage specification:

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

export interface Spec extends TurboModule {
  setItem(value: string, key: string): void;
  getItem(key: string): string | null;
  removeItem(key: string): void;
  clear(): void;
}

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

2. Configure Codegen to run​

The specification is used by the React Native Codegen tools to generate platform specific interfaces and boilerplate for us. To do this, Codegen needs to know where to find our specification and what to do with it. Update your package.json to include:

package.json
     "start": "react-native start",
     "test": "jest"
   },
   "codegenConfig": {
     "name": "NativeLocalStorageSpec",
     "type": "modules",
     "jsSrcsDir": "specs",
     "android": {
       "javaPackageName": "com.nativelocalstorage"
     }
   },
   "dependencies": {

With everything wired up for Codegen, we need to prepare our native code to hook into our generated code.

Codegen is executed through the generateCodegenArtifactsFromSchema Gradle task:

cd android
./gradlew generateCodegenArtifactsFromSchema

BUILD SUCCESSFUL in 837ms
14 actionable tasks: 3 executed, 11 up-to-date

This is automatically run when you build your Android application.

3. Write Application Code using the Turbo Native Module​

Using NativeLocalStorage, here’s a modified App.tsx that includes some text we want persisted, an input field and some buttons to update this value.

The TurboModuleRegistry supports 2 modes of retrieving a Turbo Native Module:

  • get<T>(name: string): T | null which will return null if the Turbo Native Module is unavailable.
  • getEnforcing<T>(name: string): T which will throw an exception if the Turbo Native Module is unavailable. This assumes the module is always available.
App.tsx
import React from 'react';
import {
  SafeAreaView,
  StyleSheet,
  Text,
  TextInput,
  Button,
} from 'react-native';

import NativeLocalStorage from './specs/NativeLocalStorage';

const EMPTY = '<empty>';

function App(): React.JSX.Element {
  const [value, setValue] = React.useState<string | null>(null);

  const [editingValue, setEditingValue] = React.useState<
    string | null
  >(null);

  React.useEffect(() => {
    const storedValue = NativeLocalStorage?.getItem('myKey');
    setValue(storedValue ?? '');
  }, []);

  function saveValue() {
    NativeLocalStorage?.setItem(editingValue ?? EMPTY, 'myKey');
    setValue(editingValue);
  }

  function clearAll() {
    NativeLocalStorage?.clear();
    setValue('');
  }

  function deleteValue() {
    NativeLocalStorage?.removeItem(editingValue ?? EMPTY);
    setValue('');
  }

  return (
    <SafeAreaView style={{flex: 1}}>
      <Text style={styles.text}>
        Current stored value is: {value ?? 'No Value'}
      </Text>
      <TextInput
        placeholder="Enter the text you want to store"
        style={styles.textInput}
        onChangeText={setEditingValue}
      />
      <Button title="Save" onPress={saveValue} />
      <Button title="Delete" onPress={deleteValue} />
      <Button title="Clear" onPress={clearAll} />
    </SafeAreaView>
  );
}

const styles = StyleSheet.create({
  text: {
    margin: 10,
    fontSize: 20,
  },
  textInput: {
    margin: 10,
    height: 40,
    borderColor: 'black',
    borderWidth: 1,
    paddingLeft: 5,
    paddingRight: 5,
    borderRadius: 5,
  },
});

export default App;

4. Write your Native Platform code​

With everything prepared, we're going to start writing native platform code. We do this in 2 parts:

note

This guide shows you how to create a Turbo Native Module that only works with the New Architecture. If you need to support both the New Architecture and the Legacy Architecture, please refer to our backwards compatibility guide.

Now it's time to write some Android platform code to make sure localStorage survives after the application is closed.

The first step is to implement the generated NativeLocalStorageSpec interface:

android/app/src/main/java/com/nativelocalstorage/NativeLocalStorageModule.java
package com.nativelocalstorage;

import android.content.Context;
import android.content.SharedPreferences;
import com.nativelocalstorage.NativeLocalStorageSpec;
import com.facebook.react.bridge.ReactApplicationContext;

public class NativeLocalStorageModule extends NativeLocalStorageSpec {

  private static final String NAME = "NativeLocalStorage";

  public NativeLocalStorageModule(ReactApplicationContext reactContext) {
    super(reactContext);
  }

  @Override
  public String getName() {
    return NAME;
  }

  @Override
  public void setItem(String value, String key) {
    SharedPreferences sharedPref = getReactApplicationContext().getSharedPreferences("my_prefs", Context.MODE_PRIVATE);
    SharedPreferences.Editor editor = sharedPref.edit();
    editor.putString(key, value);
    editor.apply();
  }

  @Override
  public String getItem(String key) {
    SharedPreferences sharedPref = getReactApplicationContext().getSharedPreferences("my_prefs", Context.MODE_PRIVATE);
    String username = sharedPref.getString(key, null);
    return username;
  }

  @Override
  public void removeItem(String key) {
    SharedPreferences sharedPref = getReactApplicationContext().getSharedPreferences("my_prefs", Context.MODE_PRIVATE);
    sharedPref.edit().remove(key).apply();
  }
}

Next we need to create NativeLocalStoragePackage. It provides an object to register our Module in the React Native runtime, by wrapping it as a Base Native Package:

android/app/src/main/java/com/nativelocalstorage/NativeLocalStoragePackage.java
package com.nativelocalstorage;

import com.facebook.react.BaseReactPackage;
import com.facebook.react.bridge.NativeModule;
import com.facebook.react.bridge.ReactApplicationContext;
import com.facebook.react.module.model.ReactModuleInfo;
import com.facebook.react.module.model.ReactModuleInfoProvider;

import java.util.HashMap;
import java.util.Map;

public class NativeLocalStoragePackage extends BaseReactPackage {

  @Override
  public NativeModule getModule(String name, ReactApplicationContext reactContext) {
    if (name.equals(NativeLocalStorageModule.NAME)) {
      return new NativeLocalStorageModule(reactContext);
    } else {
      return null;
    }
  }

  @Override
  public ReactModuleInfoProvider getReactModuleInfoProvider() {
    return new ReactModuleInfoProvider() {
      @Override
      public Map<String, ReactModuleInfo> get() {
        Map<String, ReactModuleInfo> map = new HashMap<>();
        map.put(NativeLocalStorageModule.NAME, new ReactModuleInfo(
          NativeLocalStorageModule.NAME,       // name
          NativeLocalStorageModule.NAME,       // className
          false, // canOverrideExistingModule
          false, // needsEagerInit
          false, // isCXXModule
          true   // isTurboModule
        ));
        return map;
      }
    };
  }
}

Finally, we need to tell the React Native in our main application how to find this Package. We call this "registering" the package in React Native.

In this case, you add it to be returned by the getPackages method.

info

Later you’ll learn how to distribute your Native Modules as npm packages, which our build tooling will autolink for you.

android/app/src/main/java/com/turobmoduleexample/MainApplication.java
package com.inappmodule;

import android.app.Application;
import com.facebook.react.PackageList;
import com.facebook.react.ReactApplication;
import com.facebook.react.ReactHost;
import com.facebook.react.ReactNativeHost;
import com.facebook.react.ReactPackage;
import com.facebook.react.defaults.DefaultNewArchitectureEntryPoint;
import com.facebook.react.defaults.DefaultReactHost;
import com.facebook.react.defaults.DefaultReactNativeHost;
import com.facebook.soloader.SoLoader;
import com.nativelocalstorage.NativeLocalStoragePackage;

import java.util.ArrayList;
import java.util.List;

public class MainApplication extends Application implements ReactApplication {

  private final ReactNativeHost reactNativeHost = new DefaultReactNativeHost(this) {
    @Override
    public List<ReactPackage> getPackages() {
      List<ReactPackage> packages = new PackageList(this).getPackages();
      // Packages that cannot be autolinked yet can be added manually here, for example:
      // packages.add(new MyReactNativePackage());
      packages.add(new NativeLocalStoragePackage());
      return packages;
    }

    @Override
    public String getJSMainModuleName() {
      return "index";
    }

    @Override
    public boolean getUseDeveloperSupport() {
      return BuildConfig.DEBUG;
    }

    @Override
    public boolean isNewArchEnabled() {
      return BuildConfig.IS_NEW_ARCHITECTURE_ENABLED;
    }

    @Override
    public boolean isHermesEnabled() {
      return BuildConfig.IS_HERMES_ENABLED;
    }
  };

  @Override
  public ReactHost getReactHost() {
    return DefaultReactHost.getDefaultReactHost(getApplicationContext(), reactNativeHost);
  }

  @Override
  public void onCreate() {
    super.onCreate();
    SoLoader.init(this, false);
    if (BuildConfig.IS_NEW_ARCHITECTURE_ENABLED) {
      // If you opted-in for the New Architecture, we load the native entry point for this app.
      DefaultNewArchitectureEntryPoint.load();
    }
  }
}

You can now build and run your code on an emulator:

npm run android