index.js

//Leave as a JS file
//https://reactnative.dev/docs/typescript#adding-typescript-to-an-existing-project

import { AppRegistry } from 'react-native';
import App from './App';
import React from 'react'
import { name as appName } from './app.json';
import 'react-native-gesture-handler' //For react-navigation
import messaging from '@react-native-firebase/messaging';
import { handleFCMMessage } from 'utils/fcmNotificationHandlers';
import codePush from "react-native-code-push";
import 'react-native-get-random-values' //https://github.com/uuidjs/uuid#getrandomvalues-not-supported
import PushNotification from "react-native-push-notification";

//We'll manage the updating and whatnot to ourselves since we want a really 
//reliable and fast update delivery
//https://manurana.medium.com/codepush-update-strategies-for-a-react-native-app-6c0d2acd4f4c
//(keep in mind emulators connected to RN server will
//never be synched with codepush sicne we don't give them api keys)
let codePushOptions = { 
  checkFrequency: codePush.CheckFrequency.MANUAL 
};

const CodePushApp = codePush(codePushOptions)(App)

messaging().setBackgroundMessageHandler(async (remoteMessage) => {
  await handleFCMMessage(remoteMessage)
});

//https://rnfirebase.io/messaging/usage#background-application-state
function HeadlessCheckedApp({ isHeadless }) {
  // If app has been "launched" in the background by iOS due to FCM, ignore
  if (isHeadless) return null;
  return <CodePushApp />;
}

// Must be outside of any component LifeCycle (such as `componentDidMount`).
// Might not be needed since we're no longer using it in our fcm handlers
// but we'll keep it in anyways
PushNotification.configure({}); 

AppRegistry.registerComponent(appName, () => HeadlessCheckedApp);