chart.js plugin for making waterfall charts

Question

I want to create a chart.js plugin to create waterfall charts.

I am new to working with chart.js. I was thinking to extend the bar-chart to create a waterfall chart.

The draw function in the bar chart controller is as follows:

draw: function(ease) {
            var me = this;
            var easingDecimal = ease || 1;
            helpers.each(me.getMeta().data, function(rectangle, index) {
                var d = me.getDataset().data[index];
                if (d !== null && d !== undefined && !isNaN(d)) {
                    rectangle.transition(easingDecimal).draw();
                }
            }, me);
        },

THe full bar chart controller js file can be found here: https://github.com/chartjs/Chart.js/tree/master/src/controllers

Answer 1

Since Chart.js v2.9.0., we can use floating bars to easily create waterfall charts. Individual bars may since be specified with the syntax [min, max].

Given an array of values [3, 5, 4, 2, 6], we need to produce the following data (last entry being the computed value for the 'Total' bar):

[[0, 3], [3, 8], [8, 12], [12, 14], [14, 20], 20]

The only additional thing left to do is defining a tooltips.callback function that computes the correct value to be shown in the tooltips.

tooltips: {
  callbacks: {
    label: (tooltipItem, data) => {
      const v = data.datasets[0].data[tooltipItem.index];
      return Array.isArray(v) ? v[1] - v[0] : v;
    }
  }
},

Please have a look at the following code sample that produces a waterfall chart out of the baseData array.

let baseData = [
 { label: 'A', value: 3 }, 
 { label: 'B', value: 5 }, 
 { label: 'C', value: 4 },
 { label: 'D', value: 2 }, 
 { label: 'E', value: 6 }
];

const labels = baseData.map(o => o.label).concat('Total');
const data = [];
let total = 0;
for (let i = 0; i < baseData.length; i++) {
  const vStart = total;
  total += baseData[i].value;
  data.push([vStart, total]);  
}
data.push(total);
const backgroundColors = data.map((o, i) => 'rgba(255, 99, 132, ' + (i + (11 - data.length)) * 0.1 + ')');

new Chart('waterfall', {
  type: 'bar',
  data: {
    labels: labels,
    datasets: [{
      data: data,
      backgroundColor: backgroundColors,
      barPercentage: 1
    }]
  },
  options: {
    responsive: true,
    maintainAspectRatio: false,
    legend: {
      display: false
    },
    tooltips: {
      callbacks: {
        label: (tooltipItem, data) => {
          const v = data.datasets[0].data[tooltipItem.index];
          return Array.isArray(v) ? v[1] - v[0] : v;
        }
      }
    },
    scales: {
      yAxes: [{
        ticks: {
          beginAtZero: true
        }
      }]
    }
  }
});

<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.9.3/Chart.min.js"></script>
<canvas id="waterfall" height="200"></canvas>

If the chart should start with the 'Total' bar, simply reverse labels, data and backgroundColors arrays as follows.

data: {
  labels: labels.reverse(),
  datasets: [{
    data: data.reverse(),
    backgroundColor: backgroundColors.reverse(),
    ...