Charts.js - Display data label only for the last value

Question

I have a line graph created with charts.js and I would like to display data labels only for the last values of the x axis. Meaning I want to show all the data points but showing the data label only for the last data point.

For example:

I was able to show data labels for every points of all the data sets using this answer: Show values on top of bars in chart.js but my aim is to display only 1 label for the last data point, and I am a bit lost here.

Here is codepen link

var TITLE = 'Trend Coronavirus per Giorno';

var X_AXIS = '';  // x-axis label and label in tooltip
var Y_AXIS = ''; // y-axis label and label in tooltip

var BEGIN_AT_ZERO = false;  // Should x-axis start from 0? `true` or `false`

var SHOW_GRID = true; // `true` to show the grid, `false` to hide
var SHOW_LEGEND = true; // `true` to show the legend, `false` to hide


$(document).ready(function() {

  // Read data file and create a chart
  $.get('https://localchef.it/csv/trendbyday.csv', function(csvString) {

    var data = Papa.parse(csvString).data;
    var timeLabels = data.slice(1).map(function(row) { return row[0]; });

    var datasets = [];
    for (var i = 1; i < data[0].length; i++) {
      datasets.push(
        {
          label: data[0][i], // column name
          data: data.slice(1).map(function(row) {return row[i]}), // data in that column
          fill: false // `true` for area charts, `false` for regular line charts
        }
      )
    }

    // Get container for the chart
    var ctx = document.getElementById('chart-container').getContext('2d');

    new Chart(ctx, {
      type: 'line',

      data: {
        labels: timeLabels,
        datasets: datasets,
      },

      options: {
        "animation": {
            "duration": 1,
                        "onComplete": function () {
                            var chartInstance = this.chart,
                                ctx = chartInstance.ctx;
                            
                            ctx.font = Chart.helpers.fontString(Chart.defaults.global.defaultFontSize, Chart.defaults.global.defaultFontStyle, Chart.defaults.global.defaultFontFamily);
                            ctx.textAlign = 'center';
                            ctx.textBaseline = 'bottom';

                            this.data.datasets.forEach(function (dataset, i) {
                                var meta = chartInstance.controller.getDatasetMeta(i);
                                meta.data.forEach(function (line) {
                                    var data = dataset.data[1];                            
                                    ctx.fillText(data, line._model.x, line._model.y - 5);
                                });
                            });
                        }
        },
        title: {
          display: true,
          text: TITLE,
          fontSize: 16,
        },

        legend: {
          display: true,
          labels: {
            boxWidth: 15,
          },
        },
        maintainAspectRatio: false,
        scales: {
          xAxes: [{
            scaleLabel: {
              display: X_AXIS !== '',
              labelString: X_AXIS
            },
            gridLines: {
              display: false,
            },
            ticks: {
              callback: function(value, index, values) {
                return value.toLocaleString();
              }
            }
          }],
          yAxes: [{
            beginAtZero: true,
            scaleLabel: {
              display: Y_AXIS !== '',
              labelString: Y_AXIS
            },
            gridLines: {
              display: SHOW_GRID,
            },
            ticks: {
              beginAtZero: BEGIN_AT_ZERO,
              callback: function(value, index, values) {
                return value.toLocaleString()
              }
            }
          }]
        },
        tooltips: {
          displayColors: true,
          mode: 'index',
          intersect: false,
          callbacks: {
            label: function(tooltipItem, all) {
              return all.datasets[tooltipItem.datasetIndex].label
                + ': ' + tooltipItem.yLabel.toLocaleString();
}
          }
        },
        plugins: {
          colorschemes: {
            scheme: 'brewer.Paired12'
          }
        }
      }
    });

  });

});

<!-- Load jQuery -->
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.4.1/jquery.min.js"></script>
  
<!-- Load Chart.js -->
<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.8.0/Chart.bundle.min.js"></script>
<script src="https://localchef.it/csv/jscolors.js"></script>

<!-- Load PapaParse to read csv files -->
<script src="https://cdnjs.cloudflare.com/ajax/libs/PapaParse/5.1.0/papaparse.min.js"></script>
<div>
  <canvas id="chart-container" style="height: 400px; width: 100%"></canvas>
</div>
<script src="script.js"></script>

Can anybody help me out?

Answer 1

This can be done with the DataLabels Plugin.

Add the JS file to your HTML:

<script src="https://cdn.jsdelivr.net/npm/[email protected]"></script>

Note: be sure to add it below the Chart.js script include.

Enable the datalabels plugin and add a custom labels formatter to the options configuration object:

plugins: {
    datalabels: {
        formatter: function(value, context) {
            if (context.dataIndex === context.dataset.data.length - 1)
            {
                return value.y;
            }
            return "";
        }
    },
}