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chart.jsonhover

Display character after y-axis data value in onhover pop up Chart.js

I'm new to Chart.js and I'm having a little bit of trouble customizing the onHover() pop up. I want to add a percent symbol after the y axis data value on the pop up, so what would be displayed will look something like this, label: value%. I have tried using scaleLabel and ticks with now luck.

Right now this is how it looks:

enter image description here

and here is my code:

let chart = new Chart(ctx, {
    type: 'line',
    data: {
      labels: dates, 
      datasets: [
        {
            label: 'Casos confirmados',
            backgroundColor: 'rgb(224, 224, 224)',
            borderColor: 'rgb(0, 0, 0)',
            data: confirmedCases
        }
      ]
    },
    options: {
        scales: {
            yAxes: [{
              gridLines: {
                drawTicks: true,
               },
                ticks: {

                  display : true,
                    // Include a percent sign in the ticks
                    callback: function(value, index, values) {
                        return value + '%';
                    }
                },
                scaleLabel: {
                    display: true,
                    labelString: '%'
                }
            }]
        }
    }
  });

If anyone could give me any pointers I would greatly appreciate it.

Solution

  • You can define tooltips.callbacks.label function inside the chart options as follows:

    tooltips: {
  callbacks: {
    label: (tooltipItem, data) => data.datasets[tooltipItem.datasetIndex].label + ': ' + tooltipItem.yLabel + '%'
  }
},

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

    let chart = new Chart('myChart', {
  type: 'line',
  data: {
    labels: ['A', 'B', 'C', 'D', 'E', ],
    datasets: [{
      label: 'Casos confirmados',
      backgroundColor: 'rgb(224, 224, 224)',
      borderColor: 'rgb(0, 0, 0)',
      data: [5, 6, 4, 3, 6]
    }]
  },
  options: {
    tooltips: {
      callbacks: {
        label: (tooltipItem, data) => data.datasets[tooltipItem.datasetIndex].label + ': ' + tooltipItem.yLabel + '%'
      }
    },
    scales: {
      yAxes: [{
        ticks: {
          beginAtZero: true,
          callback: value => value + '%'
        },
        scaleLabel: {
          display: true,
          labelString: '%'
        }
      }]
    }
  }
});
    <script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.9.4/Chart.min.js"></script>
<canvas id="myChart" height="90"></canvas>