问题描述

我有以下绘制条形图的脚本，我想在特定的 y 点上添加水平线.我正在尝试以下示例

I have the following script of drawing bar chart and I wanna add horizontal line on particular y dot. I was trying following example link and I just substituted Chart.types.Line.extend with Chart.types.Bar.extend but as a result I'm getting can not read property extend of undefined So can someone help to implement above example which in the link properly or suggest another decision

my source code without horizontal line

  var ctx = document.getElementById("myChart");
        var myChart = new Chart(ctx, {
            type: 'bar',
            data: {
                labels: ["Red", "Blue", "Yellow", "Green", "Purple", "Orange"],
                datasets: [{
                    label: '# of Votes',
                    data: [12, 19, 3, 5, 2, 3],
                    backgroundColor: [
                        'rgba(255, 99, 132, 0.2)',
                        'rgba(54, 162, 235, 0.2)',
                        'rgba(255, 206, 86, 0.2)',
                        'rgba(75, 192, 192, 0.2)',
                        'rgba(153, 102, 255, 0.2)',
                        'rgba(255, 159, 64, 0.2)'
                    ],
                    borderColor: [
                        'rgba(255,99,132,1)',
                        'rgba(54, 162, 235, 1)',
                        'rgba(255, 206, 86, 1)',
                        'rgba(75, 192, 192, 1)',
                        'rgba(153, 102, 255, 1)',
                        'rgba(255, 159, 64, 1)'
                    ],
                    borderWidth: 1
                }]
            },
            options: {
                scales: {
                    yAxes: [{
                        ticks: {
                            beginAtZero:true
                        },


                    }]
                },

            }
        });

You can use Chart.js plugins to do that. Plugins let you handle specific events such as beforeUpdate or afterDraw and are also easy to implement :

Chart.pluginService.register({
    afterDraw: function(chart) {
        // Code here will be triggered ... after the drawing
    }
});

An easy way to do it is to simply draw a line like you would you on a simple canvas element, after everything is drawn in your chart, using the lineTo method.

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