function authStateObserver()

in performance-monitoring/src/index.js [251:280]


 function authStateObserver(user) {
   if (user) { // User is signed in!
     // Get the signed-in user's profile pic and name.
     var profilePicUrl = getProfilePicUrl();
     var userName = getUserName();

     // Set the user's profile pic and name.
     userPicElement.style.backgroundImage = 'url(' + addSizeToGoogleProfilePic(profilePicUrl) + ')';
     userNameElement.textContent = userName;

     // Show user's profile and sign-out button.
     userNameElement.removeAttribute('hidden');
     userPicElement.removeAttribute('hidden');
     signOutButtonElement.removeAttribute('hidden');

     // Hide sign-in button.
     signInButtonElement.setAttribute('hidden', 'true');

     // We save the Firebase Messaging Device token and enable notifications.
     saveMessagingDeviceToken();
   } else { // User is signed out!
     // Hide user's profile and sign-out button.
     userNameElement.setAttribute('hidden', 'true');
     userPicElement.setAttribute('hidden', 'true');
     signOutButtonElement.setAttribute('hidden', 'true');

     // Show sign-in button.
     signInButtonElement.removeAttribute('hidden');
   }
 }