ChartJS: Draw vertical line at data point on chart on mouseover

Question

I can't figure out how I might draw a vertical line on a line chart at a data point when hovering over it using Chart JS. I would like the line to stay within the bounds of the chart rectangle so that it does not extend into the tick area. Any help would be appreciated!

Answer 1

There is no native functionality for this yet, rather you would have to create a chart plugin to accomplish so.

ᴘʟᴜɢɪɴ (ᴅʀᴀᴡ ᴠᴇʀᴛɪᴄᴀʟ ʟɪɴᴇ ᴏɴ ᴍᴏᴜꜱᴇᴏᴠᴇʀ ᴀᴛ ᴅᴀᴛᴀ-ᴘᴏɪɴᴛ) :

Chart.plugins.register({
   afterDatasetsDraw: function(chart) {
      if (chart.tooltip._active && chart.tooltip._active.length) {
         var activePoint = chart.tooltip._active[0],
             ctx = chart.ctx,
             y_axis = chart.scales['y-axis-0'],
             x = activePoint.tooltipPosition().x,
             topY = y_axis.top,
             bottomY = y_axis.bottom;
         // draw line
         ctx.save();
         ctx.beginPath();
         ctx.moveTo(x, topY);
         ctx.lineTo(x, bottomY);
         ctx.lineWidth = 2;
         ctx.strokeStyle = '#07C';
         ctx.stroke();
         ctx.restore();
      }
   }
});

^{* add this plugin at the beginning of your script}

ᴅᴇᴍᴏ ⧩

Chart.plugins.register({
   afterDatasetsDraw: function(chart) {
      if (chart.tooltip._active && chart.tooltip._active.length) {
         var activePoint = chart.tooltip._active[0],
            ctx = chart.ctx,
            y_axis = chart.scales['y-axis-0'],
            x = activePoint.tooltipPosition().x,
            topY = y_axis.top,
            bottomY = y_axis.bottom;
         // draw line
         ctx.save();
         ctx.beginPath();
         ctx.moveTo(x, topY);
         ctx.lineTo(x, bottomY);
         ctx.lineWidth = 2;
         ctx.strokeStyle = '#07C';
         ctx.stroke();
         ctx.restore();
      }
   }
});

var chart = new Chart(ctx, {
   type: 'line',
   data: {
      labels: ['Jan', 'Feb', 'Mar', 'Apr', 'May'],
      datasets: [{
         label: 'LINE',
         data: [3, 1, 4, 2, 5],
         backgroundColor: 'rgba(0, 119, 290, 0.2)',
         borderColor: 'rgba(0, 119, 290, 0.6)',
         fill: false
      }]
   },
   options: {
      responsive: false,
      scales: {
         yAxes: [{
            ticks: {
               beginAtZero: true
            }
         }]
      }
   }
});

<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.6.0/Chart.min.js"></script>
<canvas id="ctx" height="200"></canvas>