ChartJS multiple annotations (vertical lines)

Question

i am trying to put 2 vertical lines on a chart.JS chart using the annotations plugin. i am using the following versions: chart.js = 2.8.0 annotations plugin = 0.5.7

here's the JSFiddle

please see my code below:

var ann = ["4.35"];
var ann_labels = ["start"];
var annotations_array = ann.map(function(value, index) {
    return {
        type: 'line',
        id: 'vline' + index,
        mode: 'vertical',
        scaleID: 'x-axis-0',
        value: value,
        borderColor: 'green',
        borderWidth: 1,
        label: {
            enabled: true,
            position: "bottom",
            content: ann_labels
        }
    }
});

var ann2 = ["4.29"];
var ann_labels2 = ["stop"];
var annotations_array2 = ann2.map(function(value, index) {
    return {
        type: 'line',
        id: 'vline2' + index,
        mode: 'vertical',
        scaleID: 'x-axis-0',
        value: value,
        borderColor: 'green',
        borderWidth: 1,
        label: {
            enabled: true,
            position: "top",
            content: ann_labels2
        }
    }
});

var ctx = document.getElementById('test').getContext('2d');
var test = new Chart(ctx, {
    type: 'line',
    data: {
        labels: ["1.44","4.03","4.35","3.99","3.58","3.75","4.29","5.02","5.95","6.65"],
        datasets: [{
            data: ["1", "2", "1", "2", "1", "2", "1", "2", "1", "2"],
            yAxisID: 'A',
            backgroundColor: [
                'rgba(91, 192, 222, 0.1)',
            ],
            borderColor: [
                'rgba(0, 123, 255, 0.8)',
            ],
            borderWidth: 1.3,
        },
        {
            data: ["10", "11", "12","13","14","15","16","17",],
            yAxisID: 'B',
            backgroundColor: [
                'rgba(255, 206, 86, 0.0)',
            ],
            borderColor: [
                'rgba(217, 83, 79, 0.6)',
            ],
            borderWidth: 1.3,
        }]
    },
    options: {
        annotation: {
            drawTime: 'afterDatasetsDraw',
            annotations: annotations_array
        },
        maintainAspectRatio: true,
        scales: {
            yAxes: [{
              id: 'A',
              ticks: {
                callback: function(value, index, values) {
                        return value + ' m';
                },
                reverse: true,
              }
            },
            {
              id: 'B',
              position: 'right',
              ticks: {
                callback: function(value, index, values) {
                        return value + ' °C';
                },
                reverse: true,
              }                
            }]
          },
        elements: {
            point:{
                radius: 0,
            }
        },
        legend: {
            position: 'bottom',
            display: false,
        },
    }
});

however, i am unable to display both vertical lines (annotations_array and annotations_array2) at the same time.

everything works fine when i do this: annotations: annotations_array or this: annotations: annotations_array2 but when i try to print both arrays, it doesnt work: annotations: annotations_array, annotations_array2

I have also tried this without any luck:

annotations: [{annotations_array},{annotations_array2}]

does anyone know what am i doing wrong?

Thanks in advance!

Answer 1

You have to provide both annotations as object in 1 array, not an array containing objects containing arrays, see example:

var ann = ["4.35", "4.29"];
var ann_labels = ["start", "stop"];
var annotations_array = ann.map(function(value, index) {
  return {
    type: 'line',
    id: 'vline' + index,
    mode: 'vertical',
    scaleID: 'x-axis-0',
    value: value,
    borderColor: 'green',
    borderWidth: 1,
    label: {
      enabled: true,
      position: "bottom",
      content: ann_labels[index]
    }
  }
});

var ctx = document.getElementById('test').getContext('2d');
var test = new Chart(ctx, {
  type: 'line',
  data: {
    labels: ["1.44", "4.03", "4.35", "3.99", "3.58", "3.75", "4.29", "5.02", "5.95", "6.65"],
    datasets: [{
        data: ["1", "2", "1", "2", "1", "2", "1", "2", "1", "2"],
        yAxisID: 'A',
        backgroundColor: [
          'rgba(91, 192, 222, 0.1)',
        ],
        borderColor: [
          'rgba(0, 123, 255, 0.8)',
        ],
        borderWidth: 1.3,
      },
      {
        data: ["10", "11", "12", "13", "14", "15", "16", "17", ],
        yAxisID: 'B',
        backgroundColor: [
          'rgba(255, 206, 86, 0.0)',
        ],
        borderColor: [
          'rgba(217, 83, 79, 0.6)',
        ],
        borderWidth: 1.3,
      }
    ]
  },
  options: {
    annotation: {
      drawTime: 'afterDatasetsDraw',
      annotations: annotations_array
    },
    maintainAspectRatio: true,
    scales: {
      yAxes: [{
          id: 'A',
          ticks: {
            callback: function(value, index, values) {
              return value + ' m';
            },
            reverse: true,
          }
        },
        {
          id: 'B',
          position: 'right',
          ticks: {
            callback: function(value, index, values) {
              return value + ' °C';
            },
            reverse: true,
          }
        }
      ]
    },
    elements: {
      point: {
        radius: 0,
      }
    },
    legend: {
      position: 'bottom',
      display: false,
    },
  }
});

<h3 class="card-text"><canvas id="test"></canvas></h3>
<script src="https://cdn.jsdelivr.net/npm/chart.js@2.8.0"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/chartjs-plugin-annotation/0.5.7/chartjs-plugin-annotation.min.js"></script>

Fiddle: https://jsfiddle.net/Leelenaleee/6Ltycqfh/7/