[Chartjs]-Chart.js line chart tooltip shows wrong label when line doesn't start at first label

by

1👍

✅

Basically, the answer is to replace this:

[
    {y: 30, x: 'Jan 2019'},
    {y: 20, x: 'Apr 2019'},
    {y: 25, x: 'Jul 2019'},
]

with this:

[null, 30, 20, 25, null]

1👍

Chart.js doesn’t like date-labels as string. You should use a Date() or momentjs() object to give a date.

Using MomentJS, your graph could look something like this;

const newDate = (mdy) => moment(mdy, "MM-DD-YYYY");

var lineChartData = {
    labels: [newDate('9-1-2018'), newDate('1-1-2019'), newDate('4-1-2019'), newDate('6-1-2019'), newDate('9-1-2019')],
    datasets: [{
        label: 'Oranges',
        borderColor: 'blue',
        backgroundColor: 'orange',
        fill: false,
        data: [
            { y: 30, x: newDate('1-1-2019') },
            { y: 20, x: newDate('4-1-2019') },
            { y: 25, x: newDate('6-1-2019') }
        ],
    }]
};

window.onload = function() {
    var ctx = document.getElementById('canvas').getContext('2d');
    window.myLine = Chart.Line(ctx, {
        data: lineChartData,
        options: {
            hover: {
                mode: 'new mode'
            },
            responsive: true,
            hoverMode: 'index',
            stacked: false,
            scales: {
                yAxes: [{
                    type: 'linear',
                    display: true,
                    position: 'left'
                }],
                xAxes: [{
                    type: 'time',
                    time: {
                        displayFormats: {
                            'millisecond': 'MMM YY',
                            'second': 'MMM YY',
                            'minute': 'MMM YY',
                            'hour': 'MMM YY',
                            'day': 'MMM YY',
                            'week': 'MMM YY',
                            'month': 'MMM YY',
                            'quarter': 'MMM YY',
                            'year': 'MMM YY',
                        }
                    }
                }]
            }
        }
    });
};
<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.29.1/moment.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/chart.js@2.8.0"></script>
<canvas id="canvas" ></canvas>

(Note; the extra empty data could me removed, please take a look at the Chartjs time docs)

EDIT: Based on comments, a more complete solution, with the original data being parsed as the OP intended.

const newDate = (mdy) => moment(mdy, "MMM YYYY");
const data = {
  labels: ['Oct 2018', 'Jan 2019', 'Apr 2019', 'Jul 2019', 'Oct 2019'],
  points: [
    {y: 30, x: 'Jan 2019'},
    {y: 20, x: 'Apr 2019'},
    {y: 25, x: 'Jul 2019'}
  ]
};

var lineChartData = {
    labels: data.labels.map(l => newDate(l)),
    datasets: [{
        label: 'Oranges',
        borderColor: 'blue',
        backgroundColor: 'orange',
        fill: false,
        data: data.points.map(p => { return { ...p, x: newDate(p.x) } })
    }]
};

window.onload = function() {
    var ctx = document.getElementById('canvas').getContext('2d');
    window.myLine = Chart.Line(ctx, {
        data: lineChartData,
        options: {
            hover: {
                mode: 'new mode'
            },
            responsive: true,
            hoverMode: 'index',
            stacked: false,
            scales: {
                yAxes: [{
                    type: 'linear',
                    display: true,
                    position: 'left'
                }],
                xAxes: [{
                    type: 'time',
                    time: {
                    parser: 'MMM YYYY',
                        tooltipFormat: 'MMM YYYY',
                        displayFormats: {
                            'millisecond': 'MMM YYYY',
                            'second': 'MMM YYYY',
                            'minute': 'MMM YYYY',
                            'hour': 'MMM YYYY',
                            'day': 'MMM YYYY',
                            'week': 'MMM YYYY',
                            'month': 'MMM YYYY',
                            'quarter': 'MMM YYYY',
                            'year': 'MMM YYYY',
                        }
                    }
                }]
            }
        }
    });
};
<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.29.1/moment.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/chart.js@2.8.0"></script>
<canvas id="canvas" ></canvas>

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