expo-react-native-adapter/src/NativeModulesProxy.js

import { NativeModules } from 'react-native';

const NativeProxy = NativeModules.ExpoNativeModuleProxy;
const modulesConstantsKey = "modulesConstants";
const exportedMethodsKey = "exportedMethods";

const NativeModulesProxy = {};

if (NativeProxy) {
  Object.keys(NativeProxy[exportedMethodsKey]).forEach(moduleName => {
    NativeModulesProxy[moduleName] = NativeProxy[modulesConstantsKey][moduleName] || {};
    NativeProxy[exportedMethodsKey][moduleName].forEach(methodInfo => {
      NativeModulesProxy[moduleName][methodInfo.name] = async (...args) => {
        const { key, argumentsCount } = methodInfo;
        if (argumentsCount !== args.length) {
          throw new Error(`Arguments count mismatch, ${args.length} provided, ${argumentsCount} have been expected.`);
        }
        return await NativeProxy.callMethod(moduleName, key, args);
      };
    });

    // These are called by EventEmitter (which is a wrapper for NativeEventEmitter)
    // only on iOS and they use iOS-specific native module, EXReactNativeEventEmitter.
    //
    // On Android only {start,stop}Observing are called on the native module
    // and these should be exported as Expo methods.
    NativeModulesProxy[moduleName].addListener = (...args) =>
      NativeModules.EXReactNativeEventEmitter.addProxiedListener(moduleName, ...args);
    NativeModulesProxy[moduleName].removeListeners = (...args) =>
      NativeModules.EXReactNativeEventEmitter.removeProxiedListeners(moduleName, ...args);
  });
} else {
  console.warn(
    "No native NativeModulesProxy found among NativeModules, are you sure the expo-react-native-adapter's modules are linked properly?"
  );
}

module.exports = NativeModulesProxy;