How do you write a native module?

A native module bridges a platform capability that JavaScript cannot access directly, such as battery state, Bluetooth or a proprietary SDK. In the new architecture you write a TypeScript spec and let codegen produce the native interfaces.

import type { TurboModule } from "react-native";
import { TurboModuleRegistry } from "react-native";

export interface Spec extends TurboModule {
  getBatteryLevel(): Promise<number>;
  isLowPowerMode(): boolean;
}

export default TurboModuleRegistry.getEnforcing<Spec>("BatteryInfo");

Implementation steps

• Create the spec under a directory listed in codegenConfig
• Run codegen and implement the generated protocol in Swift or Kotlin
• Register the module with the app package or autolinking
• Keep methods small and return promises or use events for long work
• Handle errors with typed codes rather than throwing raw strings

Do not do heavy work synchronously on the JS call. A synchronous method blocks JavaScript, and a long native operation should return a promise or emit progress events. Also avoid passing large blobs across the boundary when a file URI or shared buffer would do.