onClick (datum) {
        const filter = this.keyAccessor()(datum);
        events.trigger(() => {
            this.filter(filter);
            this.redrawGroup();
        });
    }
This function is passed to d3 as the onClick handler for each chart. The default behavior is to
filter on the clicked datum (passed to the callback) and redraw the chart group.

This function can be replaced in order to change the click behavior (but first look at
@example
var oldHandler = chart.onClick;
chart.onClick = function(datum) {
  // use datum.
@param {*} datum
@return {undefined}