We are discontinuing the Google Sign-In JavaScript Platform Library for web. The library will be unavailable for download after the March 31, 2023 deprecation date. Instead, use the new Google Identity Services for Web.
By default, newly created Client IDs are now blocked from using the older Platform Library, existing Client IDs are unaffected. New Client IDs created before July 29th, 2022 can set `plugin_name` to enable use of the Google Platform Library.

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);
};