ChartJS: Draw line between two data points on hover

Question

Hi everyone, I have created the chart shown in the image.

Does anyone know how to draw a line between dataset of same index when trying to hover on either data (the red line).

I'm using ChartJS on VueJS component

Answer 1

The Plugin Core API offers a range of hooks that may be used for performing custom code. You can draw the line directly on the canvas using CanvasRenderingContext2D.stroke() .

In below code snippet, I use the afterDraw hook and draw the line in case the tooltip would be shown otherwise. Please consult addPlugin from vue-chart.js documentation to learn how to add such inline plugin in Vue.js .

 var chart = new Chart('canvas', { type: 'line', plugins: [{ afterDraw: chart => { if (chart.tooltip._active && chart.tooltip._active.length) { const ctx = chart.ctx; ctx.save(); const activePoint = chart.tooltip._active[0]; const x = activePoint.tooltipPosition().x; const yAxis = chart.scales['y-axis-0']; const value1 = chart.data.datasets[0].data[activePoint._index]; const value2 = chart.data.datasets[1].data[activePoint._index]; const y1 = yAxis.getPixelForValue(value1); const y2 = yAxis.getPixelForValue(value2); ctx.beginPath(); ctx.moveTo(x, y1); ctx.lineTo(x, y2); ctx.lineWidth = 2; ctx.strokeStyle = 'green'; ctx.stroke(); ctx.restore(); } } }], data: { labels: ['A', 'B', 'C', 'D', 'E', 'F'], datasets: [{ data: [13, 10, 12, 13, 9, 12], backgroundColor: 'rgba(255, 99, 132, 0.2)', borderColor: 'rgb(255, 99, 132)', fill: false }, { data: [10, 7, 9, 10, 6, 9], backgroundColor: 'rgba(255, 159, 64, 0.2)', borderColor: 'rgb(255, 159, 64)' } ] }, options: { legend: { display: false }, tooltips: { enabled: false }, scales: { yAxes: [{ ticks: { beginAtZero: true } }] } } });

 <script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.9.4/Chart.min.js"></script> <canvas id="canvas" height="90"></canvas>