const { register, listen } = require('push-receiver');

// First time
// Register to GCM and FCM
const credentials = await register(senderId); // You should call register only once and the store the credentials somewhere
storeCredentials(credentials) // Store credentials to use it later
const fcmToken = credentials.fcm.token; // Token to use to send notifications
sendTokenToBackendOrWhatever(fcmToken);


// Next times
const credentials = getSavedCredentials() // get your saved credentials from somewhere (file, db, etc...)
// persistentId is the id of the last notification received to avoid receiving all already received notifications on start.
const persistentId = getPersistentId() // get your last persistentId from somewhere (file, db, etc...), can be null
await listen({ ...credentials, persistentId}, onNotification);

// Called on new notification
function onNotification({ notification, persistentId : newPersistentId }) {
  savePersistentId(newPersistentId);
  // Do someting with the notification
  display(notification)
}