Dynamically changing subtitles at various drilldowns in treemap in highcharts?

Question

I have 5 levels of drilldown in my treemap, and I want to change the subtitle at every drilldown. I came across this code:

chart.setTitle({ text: drilldownTitle + e.point.name });

which works well for column charts, but I in treemap i have stored data in array format and there is no drilldown id, how can I achieve this functionality for treemap.

     $('#container').highcharts({
            series: [{
                type: "treemap",
                layoutAlgorithm: 'squarified'
}],

 subtitle: {
            text: 'Click points to drill down </a>.'
        },
        title: {
            text: 'TreeMap Sample'
        }
}],

Answer 1

Unfortunately Highcharts doesn't offer events like drillupToNode & drilldownToNode that would ease manipulating the chart's title.

Workaroud:

I add title-handling logic to drillToNode function and overwrite it:

H.seriesTypes.treemap.prototype.drillToNode = function(id, redraw) {
  var series = this,
    chart = series.chart,
    nodeMap = series.nodeMap,
    node = nodeMap[id],
    title;
  series.idPreviousRoot = series.rootNode;
  series.rootNode = id;

  if (id === '') {
    series.drillUpButton = series.drillUpButton.destroy();
    title = chart.userOptions.title.text;
  } else {
    series.showDrillUpButton((node && node.name || id));
    title = node.name;
  }

  chart.setTitle({
    text: title
  }, null, false);

  this.isDirty = true; // Force redraw
  if (pick(redraw, true)) {
    this.chart.redraw();
  }
}

Original function can be found in this link: https://github.com/highcharts/highcharts/blob/master/js/modules/treemap.src.js

point.events.click in no longer required while using this code, but chart needs to have the chart.title.text property defined initially.

Live demo: https://jsfiddle.net/BlackLabel/7toez0n5/