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You can use chart.js annotations plugin to draw horizontal lines at specific values, then you can implement a proper onHover callback (events on the whole chart) to show/hide those lines.
annotation : {
drawTime : "afterDraw",
annotations : [{
id : "line1",
type : "line",
mode : "horizontal",
scaleID : "y-axis",
value : 4.5,
borderWidth : 2,
borderColor : "red",
label : {
content : "threshold 1",
enabled : true,
position : "right"
}
}
]
},
See my fiddle exemplifying the approach: https://jsfiddle.net/beaver71/5jg4wgdh/
var data_set = [{x: 1, y: 12}, {x: 2, y: 3}, {x: 3, y: 2}, {x: 4, y: 1}, {x: 5, y: 8}, {x: 6, y: 8}, {x: 7, y: 2}, {x: 8, y: 2}, {x: 9, y: 3}, {x: 10, y: 5}, {x: 11, y: 11}, {x: 12, y: 1}];
var labels = ["JAN", "FEB", "MAR", "APR", "MAY", "JUN", "JUL", "AUG", "SEP", "OCT", "NOV", "DEC"];
var lines = [], id = 0;
var linesOn = false;
var data = {
labels: labels,
datasets: [{
label: "My First dataset",
backgroundColor: "rgba(255,99,132,0.2)",
borderColor: "rgba(255,99,132,1)",
borderWidth: 2,
hoverBackgroundColor: "rgba(255,99,132,0.4)",
hoverBorderColor: "rgba(255,99,132,1)",
data: data_set,
}]
};
var option = {
legend: false,
title: {
display: true,
},
onHover: function(evt) {
console.log("onHover", evt.type);
if (evt.type == 'mousemove' && linesOn == false) {
linesOn = true;
myLineChart.options.annotation.annotations = lines;
myLineChart.update();
} else if (evt.type == 'mouseout' && linesOn == true) {
linesOn = false;
myLineChart.options.annotation.annotations = [];
myLineChart.update();
}
var item = myLineChart.getElementAtEvent(evt);
if (item.length) {
console.log(">item", item);
console.log(">data", item[0]._index, data.datasets[0].data[item[0]._index]);
}
},
onClick: function(evt) {
var el = myLineChart.getElementAtEvent(evt);
console.log("onClick", el, evt);
},
annotation: {
drawTime: "afterDraw",
annotations: lines
},
scales: {
xAxes: [{
id: 'x-axis',
type: 'linear',
position: 'bottom',
ticks: {
max: 12,
min: 1,
stepSize: 1,
callback: function(value, index, values) {
return data.labels[index];
}
}
}],
yAxes: [{
id: 'y-axis',
type: 'linear',
}],
}
};
var myLineChart = Chart.Line('myChart', {
data: data,
options: option
});
// define two lines (these code must be after chart creation)
addLine(3.5);
addLine(7);
function addLine(value) {
id++;
var ln = {
id: "line" + id,
type: "line",
mode: "horizontal",
scaleID: "y-axis",
value: value,
borderWidth: 2,
borderColor: "red",
label: {
content: "threshold " + id,
enabled: true,
position: "right"
}
};
lines.push(ln);
}<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.7.1/Chart.bundle.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/chartjs-plugin-annotation/0.5.7/chartjs-plugin-annotation.min.js"></script>
<canvas id="myChart" width="400" height="200"></canvas>Update:
If you need to animate annotation hovering on them, here is another example:
https://jsfiddle.net/beaver71/yxy402rk/
var data_set = [{x: 1, y: 12}, {x: 2, y: 3}, {x: 3, y: 2}, {x: 4, y: 1}, {x: 5, y: 8}, {x: 6, y: 8}, {x: 7, y: 2}, {x: 8, y: 2}, {x: 9, y: 3}, {x: 10, y: 5}, {x: 11, y: 11}, {x: 12, y: 1}];
var labels = ["JAN", "FEB", "MAR", "APR", "MAY", "JUN", "JUL", "AUG", "SEP", "OCT", "NOV", "DEC"];
var lines = [], id = 0;
var linesOn = false;
var data = {
labels: labels,
datasets: [{
label: "My First dataset",
backgroundColor: "rgba(255,99,132,0.2)",
borderColor: "rgba(255,99,132,1)",
borderWidth: 2,
hoverBackgroundColor: "rgba(255,99,132,0.4)",
hoverBorderColor: "rgba(255,99,132,1)",
data: data_set,
}]
};
var option = {
legend: false,
title: {
display: true,
},
onHover: function(evt) {
var item = myLineChart.getElementAtEvent(evt);
if (item.length) {
console.log(">item", item);
console.log(">data", item[0]._index, data.datasets[0].data[item[0]._index]);
}
},
onClick: function(evt) {
var el = myLineChart.getElementAtEvent(evt);
console.log("onClick", el, evt);
},
annotation: {
drawTime: "afterDraw",
events: ['click','mouseenter','mouseleave'],
annotations: lines
},
scales: {
xAxes: [{
id: 'x-axis',
type: 'linear',
position: 'bottom',
ticks: {
max: 12,
min: 1,
stepSize: 1,
callback: function(value, index, values) {
return data.labels[index];
}
}
}],
yAxes: [{
id: 'y-axis',
type: 'linear',
}],
}
};
addLine(3.5);
addLine(7);
var myLineChart = Chart.Line('myChart', {
data: data,
options: option
});
console.log(myLineChart.annotation.elements.line1);
myLineChart.annotation.elements.line1.hidden = true;
myLineChart.update();
function addLine(value) {
id++;
var ln = {
id: "line" + id,
type: "line",
mode: "horizontal",
scaleID: "y-axis",
value: value,
borderWidth: 2,
borderColor: "rgba(0,0,255,0.3)",
label: {
content: "threshold " + id,
enabled: true,
position: "right",
backgroundColor: 'rgba(0,0,0,0.3)',
},
onMouseenter: function(e) {
console.log("onMouseenter", e, this);
this.options.borderColor = "rgba(0,0,255,0.8)";
this.options.label.backgroundColor = 'rgba(0,0,0,0.8)';
myLineChart.update();
},
onMouseleave: function(e) {
console.log("onMouseleave", e);
this.options.borderColor = "rgba(0,0,255,0.3)";
this.options.label.backgroundColor = 'rgba(0,0,0,0.3)';
myLineChart.update();
},
};
lines.push(ln);
}<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.7.1/Chart.bundle.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/chartjs-plugin-annotation/0.5.7/chartjs-plugin-annotation.min.js"></script>
<canvas id="myChart" width="400" height="200"></canvas>Source:stackexchange.com