Doing common JavaScript tasks without Redux https://medium.com/p/f23ffbbb02ae

auth.js

import '@firebase/auth';
import firebase from '@firebase/app';

const callbacks = new Set();

export default {
  signIn() {
    const provider = new firebase.auth.FacebookAuthProvider();
    return firebase.auth().signInWithPopup(provider);
  },

  signOut() {
    return firebase.auth().signOut();
  },

  showLoginDialog() {
    callbacks.forEach(cb => cb());
  },

  onShowLoginDialog(cb) {
    callbacks.add(cb);
    return () => { callbacks.delete(cb); };
  },

  onAuthStateChanged(cb) {
    firebase.auth().onAuthStateChanged(cb);
  },
};