Today we’re announcing a few updates to the Google+ JavaScript SDK APIs. These changes are backward compatible with current integrations, and are designed to make future integrations easier.

gapi.auth.signIn() triggers user sign-in and authorization in JavaScript, making it easier to integrate Google+ Sign-In with existing account creation flows.

gapi.auth.signOut() signs the current user out of your app.

A new status field indicates whether users are signed in to Google and/or your website, and a new method field describes how the sign-in occurred.

You can now specify sign-in parameters once in <meta> tags, versus passing them multiple times to multiple page elements. These page-level configuration parameters simplify your integration of Google+ Sign-In and interactive posts.

The sign-in callback is now dynamic when using page-level configuration. This makes it possible, for example, to sync your site’s user experience across multiple tabs.
Google+ JavaScript SDK APIs Updated [googleplusplatform.blogspot.com]