chart.js Line chart with different background colors for each section

Question

Lets say I have a Line chart with mon-fri for 4 weeks. I want that these 4 weeks are diveded in sections. I want the first monday to friday have a white background color. The second monday to friday a gray background. The thirth a white bg again. And the fourth weeks with monday to friday to have a gray background color. What Im talking about is the background of the graph. Is there a way to do this?

Answer 1

Chart.js clears the canvas before drawing (or redrawing) a chart.

We can jump in on this and draw our background once the chart is cleared. Just extend the Line chart and override the clear function in the initialize override.

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Preview

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Script

Chart.types.Line.extend({
    name: "LineAlt",
    initialize: function(data){
        Chart.types.Line.prototype.initialize.apply(this, arguments);

        // keep a reference to the original clear
        this.originalClear = this.clear;
        this.clear = function () {

            this.originalClear();

            // 1 x scale unit
            var unitX = this.datasets[0].points[1].x - this.datasets[0].points[0].x;

            var yTop = this.scale.startPoint;
            var yHeight = this.scale.endPoint - this.scale.startPoint;

            // change your color here
            this.chart.ctx.fillStyle = 'rgba(100,100,100,0.8)';

            // we shift it by half a x scale unit to the left because the space between gridline is actually a shared space
            this.chart.ctx.fillRect(this.datasets[0].points[5].x - 0.5 * unitX, yTop, unitX * 5, yHeight);
            this.chart.ctx.fillRect(this.datasets[0].points[15].x - 0.5 * unitX, yTop, unitX * 5, yHeight);
        }
    }
});

Then just use LineAlt instead of Line

var myNewChart = new Chart(ctx).LineAlt(data);

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Fiddle - http://jsfiddle.net/oe2606ww/

Answer 2

Some people here have requested something that works for later versions, here's my hacked together solution that works on ChartJS 2.7.2 (EDIT: Apr 2020: Also 2.9.3) and could probably be adapted. Chart.types.Line.extend used in the answer above, doesn't seem to be valid in v2.

I managed to figure this out with help from this thread to get the plugin code, and also found this thread useful for gathering co-ordinates of the data points.

With some work this fiddle should allow you to pass the label array keys as start/stop positions via the following code (where 0 and 1 are the keys):

var start = meta.data[0]._model.x;
var stop  = meta.data[1]._model.x;

You could loop this, along with the ctx.fillRect function to draw multiple rectangles.

Here's the working fiddle: http://jsfiddle.net/oe2606ww/436/

Answer 3

I combined @potatopeelings's and @v25's solutions for a chart.js v2 solution. It utilizes the format of @potatopeelings's solution, allowing to use an alternate chart type (LineAlt), and the updated implementation from @v25's solution.

Chart.controllers.LineAlt = Chart.controllers.line.extend({
    draw: function (ease) {
        if (this.chart.config.options.chartArea && this.chart.config.options.chartArea.backgroundColor) {
            var ctx = this.chart.chart.ctx;
            var chartArea = this.chart.chartArea;

            var meta = this.chart.getDatasetMeta(0);

            var start = meta.data[1]._model.x;
            var stop  = meta.data[2]._model.x;

            ctx.save();
            ctx.fillStyle = this.chart.config.options.chartArea.backgroundColor;
            ctx.fillRect(start, chartArea.top, stop - start, chartArea.bottom - chartArea.top);
            ctx.restore();
        }

        // Perform regular chart draw
        Chart.controllers.line.prototype.draw.call(this, ease);
    }
});

Then you can use the custom chart type just as in @potatopeelings's solution:

var myNewChart = new Chart(ctx, {type: 'LineAlt', data: data});