How can I draw an vertical line at a particular point on the x-axis using Chart.js?
In particular, I want to draw a line to indicate the current day on a LineChart. Here's a mockup of the chart: http://i.stack.imgur.com/VQDWR.png
How can I draw an vertical line at a particular point on the x-axis using Chart.js?
In particular, I want to draw a line to indicate the current day on a LineChart. Here's a mockup of the chart: http://i.stack.imgur.com/VQDWR.png
Update - this answer is for Chart.js 1.x, if you are looking for a 2.x answer check the comments and other answers.
You extend the line chart and include logic for drawing the line in the draw function.
Preview
HTML
<div>
<canvas id="LineWithLine" width="600" height="400"></canvas>
</div>
Script
var data = {
labels: ["JAN", "FEB", "MAR", "APR", "MAY", "JUN", "JUL", "AUG", "SEP", "OCT", "NOV", "DEC"],
datasets: [{
data: [12, 3, 2, 1, 8, 8, 2, 2, 3, 5, 7, 1]
}]
};
var ctx = document.getElementById("LineWithLine").getContext("2d");
Chart.types.Line.extend({
name: "LineWithLine",
draw: function () {
Chart.types.Line.prototype.draw.apply(this, arguments);
var point = this.datasets[0].points[this.options.lineAtIndex]
var scale = this.scale
// draw line
this.chart.ctx.beginPath();
this.chart.ctx.moveTo(point.x, scale.startPoint + 24);
this.chart.ctx.strokeStyle = '#ff0000';
this.chart.ctx.lineTo(point.x, scale.endPoint);
this.chart.ctx.stroke();
// write TODAY
this.chart.ctx.textAlign = 'center';
this.chart.ctx.fillText("TODAY", point.x, scale.startPoint + 12);
}
});
new Chart(ctx).LineWithLine(data, {
datasetFill : false,
lineAtIndex: 2
});
The option property lineAtIndex controls which point to draw the line at.
Fiddle - http://jsfiddle.net/dbyze2ga/14/
Sharing my solution for chartjs.org version 2.5. I wanted to use a plugin, to make the implementation reusable.
const verticalLinePlugin = {
getLinePosition: function (chart, pointIndex) {
const meta = chart.getDatasetMeta(0); // first dataset is used to discover X coordinate of a point
const data = meta.data;
return data[pointIndex]._model.x;
},
renderVerticalLine: function (chartInstance, pointIndex) {
const lineLeftOffset = this.getLinePosition(chartInstance, pointIndex);
const scale = chartInstance.scales['y-axis-0'];
const context = chartInstance.chart.ctx;
// render vertical line
context.beginPath();
context.strokeStyle = '#ff0000';
context.moveTo(lineLeftOffset, scale.top);
context.lineTo(lineLeftOffset, scale.bottom);
context.stroke();
// write label
context.fillStyle = "#ff0000";
context.textAlign = 'center';
context.fillText('MY TEXT', lineLeftOffset, (scale.bottom - scale.top) / 2 + scale.top);
},
afterDatasetsDraw: function (chart, easing) {
if (chart.config.lineAtIndex) {
chart.config.lineAtIndex.forEach(pointIndex => this.renderVerticalLine(chart, pointIndex));
}
}
};
Chart.plugins.register(verticalLinePlugin);
Usage is simple then:
new Chart(ctx, {
type: 'line',
data: data,
label: 'Progress',
options: options,
lineAtIndex: [2,4,8],
})
The code above inserts red vertical lines at positions 2,4 and 8, running through points of first dataset at those positions.
I had to go through the trouble of figuring out how to do something similar with ChartJS 2.0 so I thought I would share.
This is based on the new way of overriding a chart prototype as explained here: https://github.com/chartjs/Chart.js/issues/2321
var ctx = document.getElementById('income-chart');
var originalDraw = Chart.controllers.line.prototype.draw;
Chart.controllers.line.prototype.draw = function (ease) {
originalDraw.call(this, ease);
var point = dataValues[vm.incomeCentile];
var scale = this.chart.scales['x-axis-0'];
// calculate the portion of the axis and multiply by total axis width
var left = (point.x / scale.end * (scale.right - scale.left));
// draw line
this.chart.chart.ctx.beginPath();
this.chart.chart.ctx.strokeStyle = '#ff0000';
this.chart.chart.ctx.moveTo(scale.left + left, 0);
this.chart.chart.ctx.lineTo(scale.left + left, 1000000);
this.chart.chart.ctx.stroke();
// write label
this.chart.chart.ctx.textAlign = 'center';
this.chart.chart.ctx.fillText('YOU', scale.left + left, 200);
};
I'd highly recommend to use the Chartjs-Plugin-Annotation.
An example can be found at CodePen
var chartData = {
labels: ["JAN", "FEB", "MAR", "APR", "MAY", "JUN", "JUL", "AUG", "SEP", "OCT", "NOV", "DEC"],
datasets: [
{
data: [12, 3, 2, 1, 8, 8, 2, 2, 3, 5, 7, 1]
}
]
};
window.onload = function() {
var ctx = document.getElementById("canvas").getContext("2d");
new Chart(ctx, {
type: "line",
data: chartData,
options: {
annotation: {
annotations: [
{
type: "line",
mode: "vertical",
scaleID: "x-axis-0",
value: "MAR",
borderColor: "red",
label: {
content: "TODAY",
enabled: true,
position: "top"
}
}
]
}
}
});
};
Have a look here for more Details: https://stackoverflow.com/a/36431041
Here's a pen that achieves a similar effect without the chartjs-plugin-annotation, or hacking how Chart.js renders, or any other plugins: https://codepen.io/gkemmey/pen/qBWZbYM
min: 0
and max: 1
. Anytime you want to draw a vertical line, add a data object like { x: where_the_line_goes, y: 1 }
to your bar chart dataset.