FirebaseMessagingSnippet.js

const messaging = firebase.messaging();

messaging.usePublicVapidKey(YOUR_PUBLIC_VAPID_KEY_HERE);

messaging.onTokenRefresh(() => {
  messaging.getToken().then(async token => {
    const subscribeNotifications = firebase.functions().httpsCallable('subscribeNotifications');

    await subscribeNotifications({ token });
  });
});

messaging.onMessage(payload => {
  console.log('Message received.', payload);
});