[Firebase] Dealing with Popups and Redirects in a better way

auth_firebase_snippet.js

var ref = new Firebase("https://<your-firebase>.firebaseio.com");

rootRef.onAuth( function(authData){
  //It is a better way to get authData instead of get from auth callback function
  console.log(authData);
});
// prefer pop-ups, so we don't navigate away from the page
// auth callback is to handle if occur error
ref.authWithOAuthPopup("google", function(err) {
  if (err) {
    if (err.code === "TRANSPORT_UNAVAILABLE") {
      // fall-back to browser redirects, and pick up the session
      // automatically when we come back to the origin page
      ref.authWithOAuthRedirect("google", function(err) { ... });
    }
  }
});