title: How get sum of total values in stackedBar ChartJs
body: <p>I'm trying to get the sum of all values of a stackedBar and include this total in tooltip.</p>
  
  <blockquote>
    <p>Note: my datasets aren't static, this is an example</p>
  </blockquote>
  
  <pre><code>var barChartData = {
          labels: ["January", "February", "March", "April", "May", "June", "July"],
          datasets: [{
              label: 'Corporation 1',
              backgroundColor: "rgba(220,220,220,0.5)",
              data: [50, 40, 23, 45, 67, 78, 23]
          }, {
              label: 'Corporation 2',
              backgroundColor: "rgba(151,187,205,0.5)",
              data: [50, 40, 78, 23, 23, 45, 67]
          }, {
              label: 'Corporation 3',
              backgroundColor: "rgba(151,187,205,0.5)",
              data: [50, 67, 78, 23, 40, 23, 55]
          }]
  
      };
  
      window.onload = function() {
          var ctx = document.getElementById("canvas").getContext("2d");
          window.myBar = new Chart(ctx, {
              type: 'bar',
              data: barChartData,
              options: {
                  title:{
                      display:true,
                      text:"Chart.js Bar Chart - Stacked"
                  },
                  tooltips: {
                      mode: 'label',
                      callbacks: {
                         label: function(tooltipItem, data) {
                         var corporation = data.datasets[tooltipItem.datasetIndex].label;
                         var valor = data.datasets[tooltipItem.datasetIndex].data[tooltipItem.index];
                         var total = eval(data.datasets[tooltipItem.datasetIndex].data.join("+"));
                         return total+"--"+ corporation +": $" + valor.toFixed(2).replace(/(\d)(?=(\d{3})+\.)/g, '$1,');
                    }
                      }
                  },
                  responsive: true,
                  scales: {
                      xAxes: [{
                          stacked: true,
                      }],
                      yAxes: [{
                          stacked: true
                      }]
                  }
              }
          });
      };
  </code></pre>
  
  <p>Now <code>total</code> is the sum per dataset and I need the sum per stackedBar.</p>
  
  <p>Example</p>
  
  <p>Label A: value A</p>
  
  <p>Label B: value B</p>
  
  <p>Label C: value C</p>
  
  <p>TOTAL: value A + value B + value C</p>
  
  <p>It is possible to get that total value?</p>
  
  <p>Thanks, Idalia.</p>