// Options for the indicators
const indicatorOptions = {
radius: 4, borderWidth: 1, borderColor: 'red', backgroundColor: 'transparent'
};
// Override getLabelAndValue to return the interpolated value
const getLabelAndValue = Chart.controllers.line.prototype.getLabelAndValue;
Chart.controllers.line.prototype.getLabelAndValue = function(index) {
if (index === -1) {
const meta = this.getMeta();
const pt = meta._pt;
const vScale = meta.vScale;
return {
label: 'interpolated',
value: vScale.getValueForPixel(pt.y)
};
}
return getLabelAndValue.call(this, index);
}
// The interaction mode
Chart.Interaction.modes.interpolate = function (chart, e, option) {
const x = e.x;
const items = [];
const metas = chart.getSortedVisibleDatasetMetas();
for (let i = 0; i < metas.length; i++) {
const meta = metas[i];
const pt = meta.dataset.interpolate({ x }, "x");
if (pt) {
const element = new Chart.elements.PointElement({...pt, options: {...indicatorOptions}});
meta._pt = element;
items.push({element, index: -1, datasetIndex: meta.index });
} else {
meta._pt = null;
}
}
return items;
};
// Plugin to draw the indicators
Chart.register({
id: 'indicators',
afterDraw(chart) {
const metas = chart.getSortedVisibleDatasetMetas();
for (let i = 0; i < metas.length; i++) {
const meta = metas[i];
if (meta._pt) {
meta._pt.draw(chart.ctx);
}
}
},
afterEvent(chart, args) {
if (args.event.type === 'mouseout') {
const metas = chart.getSortedVisibleDatasetMetas();
for (let i = 0; i < metas.length; i++) {
metas[i]._pt = null;
}
args.changed = true;
}
}
})
var ctx = document.getElementById("myChart").getContext("2d");
var chart = new Chart(ctx, {
type: "line",
data: {
labels: ["January", "February", "March", "April", "May", "June", "July"],
datasets: [
{
fill: true,
label: "My First dataset",
backgroundColor: "rgba(132, 0, 0, 1)",
borderColor: "rgb(255, 99, 132)",
data: [0, 10, 5, 2, 20, 30, 45]
},
{
data: [30, 40, 50],
label: 'My Second Dataset',
fill: true,
backgroundColor: "lightgreen",
borderColor: "green"
}
]
},
options: {
interaction: {
mode: "interpolate",
intersect: false,
axis: "x"
},
plugins: {
tooltip: {
position: 'nearest',
displayColors: false,
}
}
},
});
.myChartDiv {
max-width: 600px;
max-height: 400px;
}
<h1>Interpolating line values</h1>
<div class="myChartDiv">
<canvas id="myChart" width="600" height="400"></canvas>
<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/3.3.2/chart.js"></script>
</div>