in performance-monitoring-start/src/index.js [242:271]
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');
}
}