title: FB.getUserID() function in Javascript SDK
body: <p>The <code>FB.getUserID()</code> function is not documented inside <a href="https://developers.facebook.com/docs/reference/javascript/" rel="nofollow">https://developers.facebook.com/docs/reference/javascript/</a></p>
  
  <p>I see many apps using it. Why is this function not documented? Is it deprecated or what?</p>