ChartJS根据下拉选择更改图表

Question

每次用户在ChartJS中选择新的图表类型时，我都试图确定重新加载画布的正确方法，但现在不会更改图表类型：

chartJs.js

 var ctx = document.getElementById("myChart").getContext("2d");
    ctx.canvas.width = 600;
    ctx.canvas.height = 200;
    var determineChart = document.getElementById("chartType");
    if( determineChart = "line") {
        var myChart = new Chart(ctx).Line(data, options);
        myChart.destroy();
    }
    else if (determineChart = "column"){
        var myChart = new Chart(ctx).Bar(data, options);

    }

index.html

<select id="chartType">
    <option value="line">Line</option>
    <option value="column">Column</option>
    <option value="area">Area</option>
    <option value="areaspline">Area Spline</option>
    <option value="pie">Pie(Test)</option>
</select>

Answer 1

因为我知道我们不能直接在Charts.js更新图表类型，所以我们必须销毁原始图表并重新绘制图表

// Define data set for the chart
    let data = [18, 10,7, 8, 18, 20, 45, 8, 0, 67];
    myData = {
        labels: ["January", "February", "March", "April", "May", "June", "July","September","October","November"],
        datasets: [{
            label: "Data, baby!",
            fill: false,
            backgroundColor: [
                "#aec7e8", "#ffbb78", "#d62728 ", "#98df8a ", "#1f77b4", "#ff7f0e ", "#2ca02c ",
                "#FF6380","#FF0000","#40E0D0","#FA8072","#339905","#98FB98","#FF8C00","#00FA9A",
                "#DC143C",
                "#FF1493",
                "#FF69B4",
                "#F08080",
                "#FFA500",
                "#FF4500",

            ],
            borderColor: 'rgb(190, 99, 255)',
            data: data,
        }]
    };

    // Default chart defined with type: 'line'
    Chart.defaults.global.defaultFontFamily = "monospace";
    var ctx = document.getElementById('my_Chart').getContext('2d');
    var myChart = new Chart(ctx, {
        type: 'line',
        data: myData
    });

    // Function runs on chart type select update
    function updateChartType() {
        // here we destroy/delete the old or previous chart and redraw it again
        myChart.destroy();
        myChart = new Chart(ctx, {
            type: document.getElementById("chartType").value,
            data: myData,
        });
    };

<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.4.0/Chart.min.js"></script>
<div class="container-div">
    <div class="controls-div">
        <select name="chartType" id="chartType" onchange="updateChartType()">
            <option value="line">Line</option>
            <option value="bar">Bar</option>
            <option value="doughnut">Doughnut</option>
            <option value="radar">Radar</option>
            <option value="polarArea">Polar Area</option>
        </select>
    </div>
    <div class="chart-container" style="position: relative; width:85vw">
        <canvas id="my_Chart"></canvas>
    </div>
</div>

Answer 2

一个问题是在条件检查中使用赋值操作符（=）而不是逻辑操作符（==或===）。此外，我不会将if/ett逻辑与可用的图表类型耦合。

var ctx = document.getElementById("myChart").getContext("2d");
 ctx.canvas.width = 600;
 ctx.canvas.height = 200;

 var dataMap = {
     'line': {
         method: 'Line',
         data: {
             labels: ["January", "February", "March", "April", "May", "June", "July"],
             datasets: [{
                 label: "My First dataset",
                 fillColor: "rgba(220,220,220,0.5)",
                 strokeColor: "rgba(220,220,220,0.8)",
                 highlightFill: "rgba(220,220,220,0.75)",
                 highlightStroke: "rgba(220,220,220,1)",
                 data: [65, 59, 80, 81, 56, 55, 40]
             }, {
                 label: "My Second dataset",
                 fillColor: "rgba(151,187,205,0.5)",
                 strokeColor: "rgba(151,187,205,0.8)",
                 highlightFill: "rgba(151,187,205,0.75)",
                 highlightStroke: "rgba(151,187,205,1)",
                 data: [28, 48, 40, 19, 86, 27, 90]
             }],
         }
     },
     'pie': {
         method: 'Pie',
         data: [{
             value: 300,
             color: "#F7464A",
             highlight: "#FF5A5E",
             label: "Red"
         }, {
             value: 50,
             color: "#46BFBD",
             highlight: "#5AD3D1",
             label: "Green"
         }, {
             value: 100,
             color: "#FDB45C",
             highlight: "#FFC870",
             label: "Yellow"
         }]
     }
 };

var currentChart;

 function updateChart() {
     if(currentChart){currentChart.destroy();}
   
     var determineChart = $("#chartType").val();

     var params = dataMap[determineChart]
     currentChart = new Chart(ctx)[params.method](params.data, {});
 }

 $('#chartType').on('change', updateChart)
 updateChart();

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script src='https://cdnjs.cloudflare.com/ajax/libs/Chart.js/1.0.2/Chart.js'></script>
<canvas id="myChart"></canvas>
<select id="chartType">
    <option value="line">Line</option>
    <option value="pie">Pie</option>
</select>