title: Google+ JavaScript API: How to detect user sign in status?
body: <p>I have deployed Google+ Sign-in Button, now I have to provide <strong>Sign-Out Button</strong>, before that, I need to know whether the user is still signed in, by which I can then show or hide this button.</p>
  
  <p>I found this documentation: <strong>gapi.auth.checkSessionState(sessionParams, callback)</strong>:
  <a href="https://developers.google.com/+/web/api/javascript?hl=en#gapiauthchecksessionstatesessionparams_callback" rel="noreferrer">https://developers.google.com/+/web/api/javascript?hl=en#gapiauthchecksessionstatesessionparams_callback</a></p>
  
  <p>Could someone demo how to use it ?</p>
  
  <p>Many thanks.</p>