How to add an offset to a dataset in Chart js

Question

I was able to add an offset to the X Labels but I would like to add an offset to all the points in the dataset. Is it possible?

This is the code I'm using:

var myChart = new Chart.Line(ctx, {
    type: 'line',
    data: {
        labels: ["JAN", "FEB", "MAR", "APR", "MAY", "JUN", "JUL", "AUG", "SEP", "OCT", "NOV", "DEC", ""],
        datasets: [{
            data: [5, 10.5, 18.2, 33.9, 121.2, 184.9, 179.9, 196.1, 158.3, 166.3, 66.4, 20.6, null],
            pointLabelFontSize : 4,
            borderWidth: 2,
            fill: false,
            lineTension: .3,
            borderColor: "#f37029",
            borderCapStyle: 'round',
            borderDash: [],
            borderDashOffset: 0.0,
            borderJoinStyle: 'bevel',
            pointBorderColor: "#f37029",
            pointBackgroundColor: "#f37029",
            pointBorderWidth: 1,
            pointHoverRadius: 4,
            pointHoverBackgroundColor: "rgba(220,220,220,1)",
            pointHoverBorderColor: "rgba(220,220,220,1)",
            pointHoverBorderWidth: 2,
            pointRadius: 4,
            pointHitRadius: 10,
            spanGaps: false,
        }]
    },
    options: {
        scales: {
            xAxes: [{
                gridLines: {
                    offsetGridLines: true,
                    display: false,
                    borderDash: [6, 2],
                    tickMarkLength:5
                },
                ticks: {
                     fontSize: 8,
                     labelOffset: 10,
                     maxRotation: 0
                }}],
            yAxes: [{
                gridLines: {
                    display:false
                },
                ticks: {
                    beginAtZero: true,
                    max: 200,
                    min: 0,
                    stepSize: 20,
                    fontSize: 8
                }
            }]
        },
        legend: {
            display: false
        },
        responsive: false,
        maintainAspectRatio: true
    }
});

I would like to apply that offset to all the points, in the image I just added an arrow to the JAN/DEC but I would like to apply it to all of them.

I tried adding a null data, the problem is that I don't want to show the first dashed grid.

Any ideas? Thanks in advance.

Answer 1

You can achieve this using Chart.js plugins. They let you handle specific events triggered during the chart creation (beforeInit, afterUpdate, afterDraw ...) and are also easy to implement :

Chart.pluginService.register({
    afterUpdate: function(chart) {
        // This will be triggered after every update of the chart
    }
});

Now you just have to loop through your dataset data model (the property used to draw charts) and add the offset you want :

Chart.pluginService.register({
    afterUpdate: function(chart) {
        // We get the dataset and set the offset here
        var dataset = chart.config.data.datasets[0];
        var offset = 20;

        // For every data in the dataset ...
        for (var i = 0; i < dataset._meta[0].data.length; i++) {
            // We get the model linked to this data
            var model = dataset._meta[0].data[i]._model;

            // And add the offset to the `x` property
            model.x += offset;

            // .. and also to these two properties
            // to make the bezier curve fits the new graph
            model.controlPointNextX += offset;
            model.controlPointPreviousX += offset;
        }
    }
});

You can see your example working on this jsFiddle and here is its result :