Chart.js 2.0 - vertical lines

Question

Can anyone tell me how to extend Chart.js v2.0. I need vertical lines in a line chart and I want to implement something similar to http://jsfiddle.net/dbyze2ga/.

Answer 1

UPDATE: See https://stackoverflow.com/a/45092928/360067 for a simpler and more robust solution using the Chart Annotations plugin.

You can extend the line type to add support for drawing a line

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Preview

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Script

var originalLineDraw = Chart.controllers.line.prototype.draw;
Chart.helpers.extend(Chart.controllers.line.prototype, {
  draw: function() {
    originalLineDraw.apply(this, arguments);

    var chart = this.chart;
    var ctx = chart.chart.ctx;

    var index = chart.config.data.lineAtIndex;
    if (index) {
      var xaxis = chart.scales['x-axis-0'];
      var yaxis = chart.scales['y-axis-0'];

      ctx.save();
      ctx.beginPath();
      ctx.moveTo(xaxis.getPixelForValue(undefined, index), yaxis.top);
      ctx.strokeStyle = '#ff0000';
      ctx.lineTo(xaxis.getPixelForValue(undefined, index), yaxis.bottom);
      ctx.stroke();
      ctx.restore();
    }
  }
});

and then

var config = {
  type: 'line',
  data: {
    labels: ...
    datasets: [
        ...
    ],
    lineAtIndex: 2
  }
};

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Fiddle - http://jsfiddle.net/mn8x6fso/