score:7

Accepted answer

You would need to either override the pie chart or create a new chart type that inherits from pie.

Here is an example of a new chart type, i have passed a new attribute called id and then the only thing that needs to be different in this chart is that when the data is being added this id needs to passed to the chart

Chart.types.Pie.extend({
    name: "PieUnique",
    addData: function (segment, atIndex, silent) {
        var index = atIndex || this.segments.length;
        this.segments.splice(index, 0, new this.SegmentArc({
            value: segment.value,
            outerRadius: (this.options.animateScale) ? 0 : this.outerRadius,
            innerRadius: (this.options.animateScale) ? 0 : (this.outerRadius / 100) * this.options.percentageInnerCutout,
            fillColor: segment.color,
            highlightColor: segment.highlight || segment.color,
            showStroke: this.options.segmentShowStroke,
            strokeWidth: this.options.segmentStrokeWidth,
            strokeColor: this.options.segmentStrokeColor,
            startAngle: Math.PI * this.options.startAngle,
            circumference: (this.options.animateRotate) ? 0 : this.calculateCircumference(segment.value),
            label: segment.label,
            //add option passed
            id: segment.id
        }));
        if (!silent) {
            this.reflow();
            this.update();
        }
    },
});

var pieData = [{
    value: 300,
    color: "#F7464A",
    highlight: "#FF5A5E",
    label: "Red",
    id: "1-upi"
}, {
    value: 50,
    color: "#46BFBD",
    highlight: "#5AD3D1",
    label: "Green",
    id: "2-upi"
}, {
    value: 100,
    color: "#FDB45C",
    highlight: "#FFC870",
    label: "Yellow",
    id: "3-upi"
}, {
    value: 40,
    color: "#949FB1",
    highlight: "#A8B3C5",
    label: "Grey",
    id: "4-upi"
}, {
    value: 120,
    color: "#4D5360",
    highlight: "#616774",
    label: "Dark Grey",
    id: "5-upi"
}

];


var ctx = document.getElementById("chart-area").getContext("2d");
window.myPie = new Chart(ctx).PieUnique(pieData);

document.getElementById("chart-area").onclick = function (evt) {
    var activePoints = window.myPie.getSegmentsAtEvent(evt);
    //you can now access the id at activePoints[0].id
    console.log(activePoints);


};
<script src="https://raw.githack.com/leighquince/Chart.js/master/Chart.js"></script>
<canvas id="chart-area" width="400"></canvas>

score:2

To get an slice that was clicked on, getElementAtEvent can be used. Worked for me!

 stackedBar(datasets) {
    var c = $("#canvas-bar");
    var ctx = c[0].getContext("2d");
    let __this = this;
    this.chart = new Chart(ctx, {
      type: 'bar',
      data: {
        labels: ["something"],
        datasets: datasets,
      },
      options: {
        onClick: function (e, item) {
          __this.onClickAction(e, item);
        },
        title: {},
        legend: {},
        scales: {}
      }
    });
  }

 onClickAction(event, elements) {
    if (elements && elements.length) {
      let selected = this.chart.getElementAtEvent(event)[0];
      let sliceIndex = selected['_datasetIndex'];
    }
  }

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