how-to-firebase-8-client-side.js

// Client-side code, in my case a web browser
firebase.auth().onAuthStateChanged(function (user) {
  this.user = user; // Set my local copy of the 'user' object
  if (user) {
    this.displayName = user.displayName;
    this.photoURL = user.photoURL;
    var userRef = firebase.database().ref('queues/login').child(user.uid);

    userRef.remove()
      .then(function () {
        return userRef.set({
          email: user.email,
          emailVerified: user.emailVerified,
          photoURL: user.photoURL,
          displayName: user.displayName,
          timestamp: new Date().toString()
        });
      });
  }
}.bind(this));