Expo Modules API: Get started

Create the local Expo module

Navigate to your project directory (the one that contains the package.json file) and run the following command. This is the recommended way to create a local Expo module.

Then, if your project doesn't have native projects generated (android and ios directories), run the following command, otherwise skip this command:

You can provide a meaningful module name in the CLI prompt. For the rest of the prompts, you can also accept the default suggestions.

Note: If you have a pre-existing ios directory in your project's root which was created using npx expo prebuild, you must reinstall the pods:

Terminal

Copy

- npx pod-install

Use the local module

Import the local module in your application, for example in App.js or App.tsx or app/index.tsx:

%%placeholder-start%%...%%placeholder-end%%
import { hello } from './modules/my-module';

export default function App() {
  return (
    <View style={styles.container}>
      <Text>{hello()}</Text>
    </View>
  );
}

Start the development sever in your terminal so that when you edit the native module and build the app in the next step, the changes will be reflected in the app:

Congratulations! You have created a local Expo module. You can now start working on it.

Tip: You can also use absolute import paths by applying these configuration changes.

Edit the module

To develop and test your module locally, let's use Android Studio and Xcode for Android and iOS.

Android

1. Open the android directory (that is generated by npx expo prebuild in step 1) from your project in Android Studio. It may take a while for Gradle to finish syncing the native directory project.
2. Once the project is synced, open modules/my-module/android/src/main/java/expo/modules/mymodule/MyModule.kt file.
3. Change hello function to return a different string, such as "Hello world! 🌎🤖" and save the file.
4. Build the app by clicking Run 'app' button from top menu bar and you will see the changes on the screen.

You have to repeat the build step anytime you make a change to the native code to the changes.

iOS

1. Open the ios directory (that is generated by npx expo prebuild in step 1) from your project in Xcode by running xed ios command.
2. Under Pods > Development Pods > MyModule, open MyModule.swift file.
3. Change hello function to return a different string, such as "Hello world! 🌎🍎" and save the file.
4. Build your app by clicking Run button from top menu bar or press ⌘ Cmd + R, you will see the changes on the screen.

You have to repeat the build step anytime you make a change to the native code to the changes.

Tip: Use npx pod-install to reinstall the pods if you add new native files to the module or when you modify expo-module.config.json.

Create the Expo module

To create a new Expo module from scratch, run the create-expo-module script as shown below. The script will ask you a few questions and then generate the native Expo module along with the example app for Android and iOS that uses your new module.

Open the module and start the development server

Navigate to the module directory and then open the Android and/or iOS example project by running the following commands:

Go to example directory and start the development sever in your terminal so that when you edit the native module and build the app in the next step, the changes will be reflected in the app:

Note: If you're using Windows, you can open the example project by opening the android directory in Android Studio, but you cannot open the iOS project files.

Edit the module

Android

1. Open my-module/android/src/main/java/expo/modules/mymodule/MyModule.kt file.
2. Change hello function to return a different string, such as "Hello world! 🌎🤖" and save the file.
3. Build the app by clicking Run 'app' button from top menu bar and you will see the changes on the screen.

You have to repeat the build step anytime you make a change to the native code to the changes.

iOS

1. Under Pods > Development Pods > MyModule, open MyModule.swift file.
2. Change hello function to return a different string, such as "Hello world! 🌎🍎" and save the file.
3. Build your app by clicking Run button from top menu bar or press ⌘ Cmd + R, you will see the changes on the screen.

You have to repeat the build step anytime you make a change to the native code to the changes.

Tip: Use npx pod-install to reinstall the pods if you add new native files to the module or when you modify expo-module.config.json.