javascript - How can I get the label onclick event by multiple graphs?

Question

I have a working chart.js on https://www.flottefeger.ch/charts.html I am trying to add an on click event to my Line chart using Chart.js. two values I can alert to pop up. But I need one more parameter. The ones which are in the label in the datasets.

It looks like that:

But now my question, how can I get which graph I have clicked? I mean the value in the label?

In my example, it could be Timmy or Siri

var ctx = document.getElementById("myChart").getContext('2d');
var myChart = new Chart(ctx, {
  type: 'line',
  data: {
    labels: ["Red", "Blue", "Yellow", "Green", "Purple", "Orange"],
    datasets: [{
        label: 'Timmy',
        data: [12, 19, 3, 5, 2, 3],
        backgroundColor: [
          'rgba(255, 99, 132, 0.2)',
          'rgba(54, 162, 235, 0.2)',
          'rgba(255, 206, 86, 0.2)',
          'rgba(75, 192, 192, 0.2)',
          'rgba(153, 102, 255, 0.2)',
          'rgba(255, 159, 64, 0.2)'
        ],
        borderColor: [
          'rgba(255,99,132,1)',
          'rgba(54, 162, 235, 1)',
          'rgba(255, 206, 86, 1)',
          'rgba(75, 192, 192, 1)',
          'rgba(153, 102, 255, 1)',
          'rgba(255, 159, 64, 1)'
        ],
        borderWidth: 1
      },

      {
        label: 'Siri',
        data: [24, 38, 6, 10, 4, 6],
        backgroundColor: [
          'rgba(255, 99, 132, 0.2)',
          'rgba(54, 162, 235, 0.2)',
          'rgba(255, 206, 86, 0.2)',
          'rgba(75, 192, 192, 0.2)',
          'rgba(153, 102, 255, 0.2)',
          'rgba(255, 159, 64, 0.2)'
        ],
        borderColor: [
          'rgba(255,99,132,1)',
          'rgba(54, 162, 235, 1)',
          'rgba(255, 206, 86, 1)',
          'rgba(75, 192, 192, 1)',
          'rgba(153, 102, 255, 1)',
          'rgba(255, 159, 64, 1)'
        ],
        borderWidth: 1
      },


    ]
  },
  options: {
    scales: {
      yAxes: [{
        ticks: {
          beginAtZero: true
        }
      }]
    }
  },



});

/* https://github.com/chartjs/Chart.js/issues/2292 */
document.getElementById("myChart").onclick = function(evt) {
  var activePoints = myChart.getElementsAtEventForMode(evt, 'point', myChart.options);
  var firstPoint = activePoints[0];
  var label = myChart.data.labels[firstPoint._index];
  var value = myChart.data.datasets[firstPoint._datasetIndex].data[firstPoint._index];
  alert(label + ": " + value);
};

<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.7.2/Chart.bundle.js"></script>
<h1>chart.js, click on data demo</h1>
<canvas id="myChart"></canvas>

Answer 1

You can change your onclick function as follows:

document.getElementById("myChart").onclick = function(evt) {
  const datasetIndex = myChart.getElementAtEvent(event)[0]._datasetIndex;
  if (datasetIndex >= 0) {
    ...
    alert(myChart.data.datasets[datasetIndex].label + '
' + label + ": " + value);
  }
};

Please take a look at your amended code and see how it works.

var ctx = document.getElementById("myChart").getContext('2d');
var myChart = new Chart(ctx, {
  type: 'line',
  data: {
    labels: ["Red", "Blue", "Yellow", "Green", "Purple", "Orange"],
    datasets: [{
        label: 'Timmy',
        data: [12, 19, 3, 5, 2, 3],
        backgroundColor: [
          'rgba(255, 99, 132, 0.2)',
          'rgba(54, 162, 235, 0.2)',
          'rgba(255, 206, 86, 0.2)',
          'rgba(75, 192, 192, 0.2)',
          'rgba(153, 102, 255, 0.2)',
          'rgba(255, 159, 64, 0.2)'
        ],
        borderColor: [
          'rgba(255,99,132,1)',
          'rgba(54, 162, 235, 1)',
          'rgba(255, 206, 86, 1)',
          'rgba(75, 192, 192, 1)',
          'rgba(153, 102, 255, 1)',
          'rgba(255, 159, 64, 1)'
        ],
        borderWidth: 1
      },
      {
        label: 'Siri',
        data: [24, 38, 6, 10, 4, 6],
        backgroundColor: [
          'rgba(255, 99, 132, 0.2)',
          'rgba(54, 162, 235, 0.2)',
          'rgba(255, 206, 86, 0.2)',
          'rgba(75, 192, 192, 0.2)',
          'rgba(153, 102, 255, 0.2)',
          'rgba(255, 159, 64, 0.2)'
        ],
        borderColor: [
          'rgba(255,99,132,1)',
          'rgba(54, 162, 235, 1)',
          'rgba(255, 206, 86, 1)',
          'rgba(75, 192, 192, 1)',
          'rgba(153, 102, 255, 1)',
          'rgba(255, 159, 64, 1)'
        ],
        borderWidth: 1
      },
    ]
  },
  options: {
    scales: {
      yAxes: [{
        ticks: {
          beginAtZero: true
        }
      }]
    }
  },
});

document.getElementById("myChart").onclick = function(evt) {
  const datasetIndex = myChart.getElementAtEvent(event)[0]._datasetIndex;
  if (datasetIndex >= 0) {
    var activePoints = myChart.getElementsAtEventForMode(evt, 'point', myChart.options);
    var firstPoint = activePoints[0];
    var label = myChart.data.labels[firstPoint._index];

    var value = myChart.data.datasets[firstPoint._datasetIndex].data[firstPoint._index];
    alert(myChart.data.datasets[datasetIndex].label + '
' + label + ": " + value);
  }
};

<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.9.4/Chart.min.js"></script>
<canvas id="myChart"></canvas>