charts-8.x-4.x-dev/modules/charts_api_example/js/charts_api_example_js_override.js

(function (Drupal) {
  Drupal.charts_api_example = Drupal.charts_api_example || {};
  // PLEASE NOTE: this example is structured to work for Highcharts, but you
  // do the same thing for any of the charting libraries.
  Drupal.charts_api_example.highchartsTooltipFormatter = function () {
    return `The value for <b>${this.x}</b> is <b>${this.y}</b>`;
  };

  Drupal.behaviors.chartsApiExampleCharts = {
    attach() {
      const chartContainer = document.getElementById('exampleidjs');
      chartContainer.addEventListener(
        'drupalChartsConfigsInitialization',
        function (e) {
          const data = e.detail;
          const id = data.drupalChartDivId;
          // Change the background of the chart to green.
          data.chart.backgroundColor = 'green';
          // Replace the tooltip formatter.
          data.tooltip.formatter =
            Drupal.charts_api_example.highchartsTooltipFormatter;
          Drupal.Charts.Contents.update(id, data);
        },
      );
    },
  };
})(Drupal);