dojox.cometd.unsubscribe("/chat/demo/" + this.roomId, this, "_chat");
dojox.cometd.publish("/chat/demo/" + this.roomId, { user: this._username, leave: true, chat : this._username+" has left the chat."});
// switch the input form back to login modethis.joining.className='';
this.joined.className='hidden';
this.username.focus();
this._username=null;