Agent skill
expo-module
Guide for writing Expo native modules and views using the Expo Modules API (Swift, Kotlin, TypeScript). Covers module definition DSL, native views, shared objects, config plugins, lifecycle hooks, autolinking, and type system. Use when building or modifying native modules for Expo.
Install this agent skill to your Project
npx add-skill https://github.com/expo/skills/tree/main/plugins/expo/skills/expo-module
SKILL.md
Writing Expo Modules
Complete reference for building native modules and views using the Expo Modules API. Covers Swift (iOS), Kotlin (Android), and TypeScript.
When to Use
- Creating a new Expo native module or native view
- Adding native functionality (camera, sensors, system APIs) to an Expo app
- Wrapping platform SDKs for React Native consumption
- Building config plugins that modify native project files
References
Consult these resources as needed:
references/
native-module.md Module definition DSL: Name, Function, AsyncFunction, Property, Constant, Events, type system, shared objects
native-view.md Native view components: View, Prop, EventDispatcher, view lifecycle, ref-based functions
lifecycle.md Lifecycle hooks: module, iOS app/AppDelegate, Android activity/application listeners
config-plugin.md Config plugins: modifying Info.plist, AndroidManifest.xml, reading values in native code
module-config.md expo-module.config.json fields and autolinking configuration
Quick Start
Create a Local Module (in existing app)
npx create-expo-module@latest --local
Generated structure:
modules/
my-module/
android/
ios/
src/
expo-module.config.json
index.ts
Create a Standalone Module (for publishing)
npx create-expo-module@latest my-module
Minimal Module
The Swift and Kotlin DSL share the same structure. Both platforms are shown here for reference — in other reference files, Swift is shown as the primary language unless the Kotlin pattern meaningfully differs.
Swift (iOS):
import ExpoModulesCore
public class MyModule: Module {
public func definition() -> ModuleDefinition {
Name("MyModule")
Function("hello") { (name: String) -> String in
return "Hello \(name)!"
}
}
}
Kotlin (Android):
package expo.modules.mymodule
import expo.modules.kotlin.modules.Module
import expo.modules.kotlin.modules.ModuleDefinition
class MyModule : Module() {
override fun definition() = ModuleDefinition {
Name("MyModule")
Function("hello") { name: String ->
"Hello $name!"
}
}
}
TypeScript:
import { requireNativeModule } from "expo";
const MyModule = requireNativeModule("MyModule");
export function hello(name: string): string {
return MyModule.hello(name);
}
expo-module.config.json
{
"platforms": ["android", "apple"],
"apple": {
"modules": ["MyModule"]
},
"android": {
"modules": ["expo.modules.mymodule.MyModule"]
}
}
Note: iOS uses just the class name; Android uses the fully-qualified class name (package + class). See references/module-config.md for all fields.
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