We are discontinuing the Google Sign-In JavaScript Platform Library for web. For authentication and user sign-in, use the new Google Identity Services SDKs for both Web and Android instead.

Monitoring the user's session state

After the Google Sign-In client has been initialized, you can attach handlers that check various attributes and methods of the client to determine the user's session state. You can use information returned by the client object to help sync your site's user experience across multiple tabs and devices for your user.

The following code demonstrates using the 2.0 client method attachClickHandler to create a callback that either silently finishes sign-in for the user, or prompts the user to re-authorize based on the state of the user's session.

/**
 * The Sign-In client object.
 */
var auth2;

/**
 * Initializes the Sign-In client.
 */
var initClient = function() {
    gapi.load('auth2', function(){
        /**
         * Retrieve the singleton for the GoogleAuth library and set up the
         * client.
         */
        auth2 = gapi.auth2.init({
            client_id: 'CLIENT_ID.apps.googleusercontent.com'
        });

        // Attach the click handler to the sign-in button
        auth2.attachClickHandler('signin-button', {}, onSuccess, onFailure);
    });
};

/**
 * Handle successful sign-ins.
 */
var onSuccess = function(user) {
    console.log('Signed in as ' + user.getBasicProfile().getName());
 };

/**
 * Handle sign-in failures.
 */
var onFailure = function(error) {
    console.log(error);
};