code: function _onClick(d) {
    if(!_scheduledClickId) {
      _scheduledClickId = setTimeout(_scheduledClick.bind(this, d, d3.event.target), 200);
    }
  }
docs: Schedules an onclick handler. If double click event is not triggered the handler
  will be called in 200ms.
  @param d {DataNode} Data of the clicked element