如何在chartjs中悬停时呈现垂直线

Here is a working example - https://jsfiddle.net/s9gyynxp/5/

var ctx = document.getElementById("myChart");
var myChart = new Chart(ctx, {
    type: 'line',
    data: {
        labels: ["Red", "Blue", "Yellow", "Green", "Purple", "Orange"],
        datasets: [{
            label: '# of Votes',
            data: [12, 19, 3, 5, 2, 3]
        }]
    }
});

// Hook into main event handler
var parentEventHandler = Chart.Controller.prototype.eventHandler;
Chart.Controller.prototype.eventHandler = function() {
    var ret = parentEventHandler.apply(this, arguments);

    // Draw the vertical line here
    var eventPosition = Chart.helpers.getRelativePosition(arguments[0], this.chart);
    this.chart.ctx.beginPath();
    this.chart.ctx.moveTo(eventPosition.x, 30);
    this.chart.ctx.strokeStyle = "#ff0000";
    this.chart.ctx.lineTo(eventPosition.x, 340);
    this.chart.ctx.stroke();

    return ret;
};

注意我已经看到了其他解决方案，其中在图表画布顶部使用了第二个画布层 - 我认为这不是我的选择，因为我需要垂直线出现在图表顶部，但在我将实施的自定义工具提示下方.

...
this.clear();
this.draw();
...