How to display Line Chart dataset point labels with Chart.js?

Question

I have a design requirement to display a line chart with 5 datasets of trends data. Each data value along the stroke lines need to be showing a data value label at its respe

Answer 1

Here's how to do it based on the example provided on github. It looks similar to your solution...

// Define a plugin to provide data labels
Chart.plugins.register({
    afterDatasetsDraw: function(chart, easing) {
        // To only draw at the end of animation, check for easing === 1
        var ctx = chart.ctx;
        chart.data.datasets.forEach(function (dataset, i) {
            var meta = chart.getDatasetMeta(i);
            if (!meta.hidden) {
                meta.data.forEach(function(element, index) {
                    // Draw the text in black, with the specified font
                    ctx.fillStyle = 'rgb(0, 0, 0)';
                    var fontSize = 16;
                    var fontStyle = 'normal';
                    var fontFamily = 'Helvetica Neue';
                    ctx.font = Chart.helpers.fontString(fontSize, fontStyle, fontFamily);
                    // Just naively convert to string for now
                    var dataString = dataset.data[index].toString();
                    // Make sure alignment settings are correct
                    ctx.textAlign = 'center';
                    ctx.textBaseline = 'middle';
                    var padding = 5;
                    var position = element.tooltipPosition();
                    ctx.fillText(dataString, position.x, position.y - (fontSize / 2) - padding);
                });
            }
        });
    }
});

From Code: https://github.com/chartjs/Chart.js/blob/master/samples/advanced/data-labelling.html

Example: http://www.chartjs.org/samples/latest/advanced/data-labelling.html

You can also define plugins inline to the chart instead of globally...

var chart = new Chart(ctx, {
    plugins: [{
        afterDatasetsDraw: ...
    }]
});

Answer 2

Updated code for @JBMcClure solution:

        var data = {
            labels: ["","Jun 2013","Jul 2013","Aug 2013","Sep 2013","Oct 2013","Nov 2013","Dec 2013","Jan 2014","Feb 2014","Mar 2014","Apr 2014","May 2014"],
            datasets: [
                {
                    label: "hemoglobin_1",
                    fillColor: "transparent",
                    strokeColor: "#65204c",
                    pointColor: "#65204c",
                    pointHighlightStroke: "#FFF",
                    data: [null,5.7,5.7,5.8,5.7,5.8,5.7,5.9,6.7,6.7,6.5,6.4,6.4]
                },
                {
                    label: "hemoglobin_2",
                    fillColor: "transparent",
                    strokeColor: "#ed7141",
                    pointColor: "#ed7141",
                    pointHighlightStroke: "#FFF",
                    data: [null,15.5,15.5,15.6,15.2,15.6,15.1,15.8,17,17.4,16.8,16.4,16.4]
                },
                {
                    label: "hemoglobin_3",
                    fillColor: "transparent",
                    strokeColor: "#de4760",
                    pointColor: "#de4760",
                    pointHighlightStroke: "#FFF",
                    data: [null,37.1,37,37.2,37.6,36.9,37.6,36.8,37.6,38,37.5,39.1,37.5]
                },
                {
                    label: "hemoglobin_4",
                    fillColor: "transparent",
                    strokeColor: "#fdcf7e",
                    pointColor: "#fdcf7e",
                    pointHighlightStroke: "#FFF",
                    data: [null,29.9,30.4,29.5,29.6,30.2,29.4,29.8,26.9,27,28.5,26.8,28.5]
                },
                {
                    label: "hemoglobin_5",
                    fillColor: "transparent",
                    strokeColor: "#a33a59",
                    pointColor: "#a33a59",
                    pointHighlightStroke: "#FFF",
                    data: [null,11.8,11.4,11.9,11.9,11.5,12.2,11.7,11.8,10.9,10.7,11.3,11.3]
                }
            ]
        };

        var options = {
            type: 'line',
            data: data,
            options: {
                responsive: true,
                scaleOverride: true,
                scaleSteps: 10,
                scaleStepWidth: 5,
                scaleStartValue: 0,
                showTooltips: false,
                pointDot: true,
                pointDotRadius : 6,
                datasetStrokeWidth : 3,
                bezierCurve : false,
                scaleShowHorizontalLines: false,
                scaleGridLineWidth : 2,
                scaleGridLineColor : "#EEEEEE",
                scaleLineWidth: 3,
                scaleLineColor: "#000000",
                scaleFontFamily: '"Gotham Book",sans-serif',
                scaleFontSize: 18,
                onAnimationProgress: function() { drawDatasetPointsLabels() },
                onAnimationComplete: function() { drawDatasetPointsLabels() }
            }
        };
        var ctx = document.getElementById('myChart').getContext('2d');
        var Trends = new Chart(ctx, options);

        function drawDatasetPointsLabels() {
            ctx.font = '.9rem "Gotham Book",sans-serif';
            ctx.fontWeight = 'bold';
            ctx.fillStyle = '#AAA';
            ctx.textAlign="center";
            $(Trends.datasets).each(function(idx,dataset){
                $(dataset.points).each(function(pdx,pointinfo){
                    if ( pointinfo.value !== null ) {
                        ctx.fillText(pointinfo.value,pointinfo.x,pointinfo.y - 15);
                    }
                });
            });
        }

@JBMcClure Here is an updated working link:

https://jsfiddle.net/s9eannLh/177/

Answer 3

In case anyone comes here looking for this as I did recently, there's a new plug in available.

https://github.com/chartjs/chartjs-plugin-datalabels

Answer 4

I was able to finally find the solution to this question.

I realized I had access to the chart object within the DOM:

Trends.datasets

Within each of the five datasets there was a points object containing x & y positions:

Trends.datasets[0..4].points

So I parsed through the points with a callback utilizing the global configuration functions in Chart.js:

    // Function - Will fire on animation progression.
     onAnimationProgress: function(){},

   // Function - Will fire on animation completion.
    onAnimationComplete: function(){}

I found that I had to use onAnimationComplete with responsive: true because the point labels would get wiped out on a resize event.

Once I found the points within the callback, I simply wrote the labels I wanted onto the canvas.

My additions to the code were:

var options = {
    onAnimationProgress: function() { drawDatasetPointsLabels() },
    onAnimationComplete: function() { drawDatasetPointsLabels() }
}

With the added function:

    function drawDatasetPointsLabels() {
            ctx.font = '.9rem "Gotham Book",sans-serif';
            ctx.fillStyle = '#AAA';
            ctx.textAlign="center";
            $(Trends.datasets).each(function(idx,dataset){
                $(dataset.points).each(function(pdx,pointinfo){
                    // First dataset is shifted off the scale line. 
                    // Don't write to the canvas for the null placeholder.
                    if ( pointinfo.value !== null ) { 
                        ctx.fillText(pointinfo.value,pointinfo.x,pointinfo.y - 15);
                    }
                });
            });         
         }

So here is the entire code source along with the new code providing the solution:

    var data = {
                labels: ["","Jun 2013","Jul 2013","Aug 2013","Sep 2013","Oct 2013","Nov 2013","Dec 2013","Jan 2014","Feb 2014","Mar 2014","Apr 2014","May 2014"],
                datasets: [
                    {
                        label: "hemoglobin_1",
                        fillColor: "transparent",
                        strokeColor: "#65204c",
                        pointColor: "#65204c",
                        pointHighlightStroke: "#FFF",
                        data: [null,5.7,5.7,5.8,5.7,5.8,5.7,5.9,6.7,6.7,6.5,6.4,6.4]
                    },
                    {
                        label: "hemoglobin_2",
                        fillColor: "transparent",
                        strokeColor: "#ed7141",
                        pointColor: "#ed7141",
                        pointHighlightStroke: "#FFF",
                        data: [null,15.5,15.5,15.6,15.2,15.6,15.1,15.8,17,17.4,16.8,16.4,16.4]
                    },                    
                    {
                        label: "hemoglobin_3",
                        fillColor: "transparent",
                        strokeColor: "#de4760",
                        pointColor: "#de4760",
                        pointHighlightStroke: "#FFF",
                        data: [null,37.1,37,37.2,37.6,36.9,37.6,36.8,37.6,38,37.5,39.1,37.5]
                    },
                    {
                        label: "hemoglobin_4",
                        fillColor: "transparent",
                        strokeColor: "#fdcf7e",
                        pointColor: "#fdcf7e",                          
                        pointHighlightStroke: "#FFF",
                        data: [null,29.9,30.4,29.5,29.6,30.2,29.4,29.8,26.9,27,28.5,26.8,28.5]
                     },                                        
                    {
                        label: "hemoglobin_5",
                        fillColor: "transparent",
                        strokeColor: "#a33a59",
                        pointColor: "#a33a59",
                        pointHighlightStroke: "#FFF",
                        data: [null,11.8,11.4,11.9,11.9,11.5,12.2,11.7,11.8,10.9,10.7,11.3,11.3]
                    }
                ]
            };

    var options = {
                responsive: true,
                scaleOverride: true,
                scaleSteps: 10,
                scaleStepWidth: 5,
                scaleStartValue: 0,
                showTooltips: false,
                pointDot: true,
                pointDotRadius : 6,
                datasetStrokeWidth : 3,
                bezierCurve : false,
                scaleShowHorizontalLines: false,
                scaleGridLineWidth : 2,
                scaleGridLineColor : "#EEEEEE",
                scaleLineWidth: 3,
                scaleLineColor: "#000000",
                scaleFontFamily: '"Gotham Book",sans-serif',
                scaleFontSize: 18,
                onAnimationProgress: function() { drawDatasetPointsLabels() },
                onAnimationComplete: function() { drawDatasetPointsLabels() }                    
            }
            var ctx = $("#myChart").get(0).getContext("2d");
            var Trends = new Chart(ctx).Line(data, options);            

        function drawDatasetPointsLabels() {
            ctx.font = '.9rem "Gotham Book",sans-serif';
            ctx.fillStyle = '#AAA';
            ctx.textAlign="center";
            $(Trends.datasets).each(function(idx,dataset){
                // First dataset is shifted off the scale line. 
                // Don't write to the canvas for the null placeholder.
                $(dataset.points).each(function(pdx,pointinfo){
                    if ( pointinfo.value !== null ) {
                        ctx.fillText(pointinfo.value,pointinfo.x,pointinfo.y - 15);
                    }
                });
            });         
        }

Here is the original problematic version on jsfiddle: http://jsfiddle.net/s9eannLh

[Updated link] And here is the updated solution on jsfiddle: https://jsfiddle.net/s9eannLh/82/

Thanks all!