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✅
Plugins are a very common way to add custom functionality to ChartJS. It allows us to manipulate event, using hooks offered by a plugin object.
In this simple example, we will create a plugin with ID horizontalLines. Then, we will call the afterDraw hook to render horizontal lines, which is called after the chart has been rendered.
const $canvas = document.getElementById('chart')
const plugin = {
id: 'horizontalLines',
defaults: {
lines: []
},
afterDraw: (chart, _, options) => {
const { ctx } = chart
const { left, right } = chart.chartArea
const lines = options.lines
if (!lines) return
for (const line of lines) {
const scale = chart.scales.y
const width = line.width || 1
const color = line.color || 'rgba(169,169,169, .6)'
const value = line.value ? scale.getPixelForValue(line.value) : 0
const label = line.label || null
if (value) {
ctx.beginPath()
ctx.lineWidth = width
ctx.moveTo(left, value)
ctx.lineTo(right, value)
ctx.strokeStyle = color
ctx.stroke()
}
if (label) {
ctx.fillStyle = color
ctx.fillText(label, right - label.length*5, value + width)
}
}
return
}
}
const data = {
labels: ['January', 'February', 'March', 'April', 'May', 'June', 'July'],
datasets: [{
data: [65, 59, 80, 81, 56, 55, 40],
label: 'Dataset01',
fill: false,
lineTension: 0.1,
backgroundColor: 'rgba(75,192,192,0.4)',
borderColor: 'rgba(75,192,192,1)',
},]
}
Chart.register(plugin)
const chart = new Chart($canvas, {
type: 'line',
data: data,
options: {
maintainAspectRatio: false,
plugins: {
'horizontalLines': {
lines: [{
value: 75.8,
color: 'red',
label: 'upper',
},
{
value: 62.3,
color: 'lime',
label: 'avg',
},
{
value: 48.8,
color: 'blue',
label: 'lower',
}]
},
},
}
}).container {
position: relative;
width: 90vw;
}<div class="container">
<canvas id="chart"></canvas>
</div>
<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/3.9.1/chart.min.js"></script>3👍
chartInstance.chart is undefined. Not sure is that a migration issue to chart.js ver 3.0…
Try the following:
<!DOCTYPE html>
<html lang="en">
<head>
<!-- <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script> -->
<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/3.0.0-beta.6/chart.js"></script>
<style>
.container{
position: relative;
width: 50vw;
}
</style>
</head>
<body>
<canvas id="myChart" class="container"></canvas>
<script>
var canvas = document.getElementById("myChart");
var ctx = canvas.getContext("2d");
var horizonalLinePlugin = {
id: 'horizontalLine',
afterDraw: function(chartInstance) {
var yScale = chartInstance.scales["y"];
// chartInstance.chart is undefined
//var canvas = chartInstance.chart;
// console.log(canvas);
// var ctx = canvas.ctx;
var index;
var line;
var style;
if (chartInstance.options.horizontalLine) {
for (index = 0; index < chartInstance.options.horizontalLine.length; index++) {
line = chartInstance.options.horizontalLine[index];
if (!line.style) {
style = "rgba(169,169,169, .6)";
} else {
style = line.style;
}
if (line.y) {
yValue = yScale.getPixelForValue(line.y);
} else {
yValue = 0;
}
ctx.lineWidth = 3;
if (yValue) {
ctx.beginPath();
ctx.moveTo(0, yValue);
ctx.lineTo(canvas.width, yValue);
ctx.strokeStyle = style;
ctx.stroke();
}
if (line.text) {
ctx.fillStyle = style;
ctx.fillText(line.text, 0, yValue + ctx.lineWidth);
}
}
return;
}
}
};
var data = {
labels: ["January", "February", "March", "April", "May", "June", "July"],
datasets: [{
label: "MyDataset01",
fill: false,
lineTension: 0.1,
backgroundColor: "rgba(75,192,192,0.4)",
borderColor: "rgba(75,192,192,1)",
data: [65, 59, 80, 81, 56, 55, 40],
},
]
};
//When uncommenting below line, graph is created without horizontal lines
Chart.register(horizonalLinePlugin);
var myChart = new Chart(ctx, {
type: 'line',
data: data,
options: {
"horizontalLine": [{
"y": 75.8,
"style": "#ff0000",
"text": "upper-limit"
}, {
"y": 62.3,
"style": "#00ff00",
"text": "avg"
}, {
"y": 48.8,
"style": "#0000ff",
"text": "lower-limit"
}],
}
});
</script>
here is the code above in Jsfiddle – working!
0👍
I was facing the same issue when using chartjs 3.0. I used the following code to get the horizontal line displayed
var horizonalLinePlugin = {
id : 'horizontalLine',
afterDraw: function (chartInstance) {
// var yScale = chartInstance.scales["y-axis-0"];
var yScale = chartInstance.scales['y'];
// var canvas = chartInstance.chart;
var canvas = chartInstance.canvas;
var ctx = chartInstance.ctx;
var index;
var line;
var style;
var yValue;
if (chartInstance.config._config.options.horizontalLine) {
for (index = 0; index < chartInstance.config._config.options.horizontalLine.length; index++) {
line = chartInstance.config._config.options.horizontalLine[index];
if (!line.style) {
style = "rgba(169,169,169, .6)";
} else {
style = line.style;
}
if (line.y) {
yValue = yScale.getPixelForValue(line.y);
} else {
yValue = 0;
}
ctx.lineWidth = 3;
if (yValue) {
ctx.beginPath();
ctx.moveTo(20, yValue);
// ctx.moveTo(0, yValue);
ctx.lineTo(canvas.width, yValue);
ctx.strokeStyle = style;
ctx.stroke();
}
if (line.text) {
ctx.fillStyle = style;
ctx.fillText(line.text, 0, yValue + ctx.lineWidth);
}
}
return;
};
}
};
Chart.register(horizonalLinePlugin);
Source:stackexchange.com