can't log out of facebook from App

I'm trying to logout of facebook from my App using the following code below, but i'm still logged in (and my alert does not execute)

also note, this is an external App, using the facebook API.

any ideas?

FB_RequireFeatures(
  ["Api"],
  function(){

   FB.Facebook开发者_运维百科.init(api_key, channel_path);
   var api = FB.Facebook.apiClient;
   FB.Connect.logout(function(){alert("logged out!");})

  }
 );

With the new JavaScript API, you can do:

FB.logout()