code: function _logoutFacebook(successCallback, errorCallback) {
      var $this = this;
  
      return Facebook.logout().then(function () {
  
        // If successful (always), also logout from Evrythng.
        return _logoutEvrythng.call($this, successCallback, errorCallback);
  
      });
    }
docs: Logging out with Facebook, logs out out from Facebook and also from Evrythng.