我正在編寫一個表達每日圖表的圖表。我想通過選擇標簽更改圖表。所以，我使用 javascript onchange。但是，它在第一次嘗試時有效，但在第二次嘗試時無效。https://jsfiddle.net/7eqn02yu/這是我的代碼 JS 小提琴。這是代碼。函數每次運行如何？<script src="https://cdnjs.cloudflare.com/ajax/libs/jspdf/1.5.3/jspdf.min.js"></script><button id="export-pdf">Export PDF</button><div id="map"></div><script src="./index.js"></script><script src="https://code.highcharts.com/highcharts.js"></script><select id="mySelect"><option value="0">mon</option><option value="1">tues</option><option value="2">wed</option><option value="3">thr</option></select><div id="container" style="height: 400px; width: 500px"></div><script type="text/javascript">const chart = Highcharts.chart('container', {    plotOptions: {        series: {            point: {            }        }    },    series: [{        data: [29.9, 71.5, 106.4, 129.2, 144.0, 176.0, 135.6, 148.5, 216.4, 194.1, 95.6, 54.4]    }]});document.getElementById("mySelect").onchange = function () { myFunction() };function myFunction() {    var x = document.getElementById("mySelect").value;    if (x = 0) {        const series = chart.series[0];        if (series.data.length) {            chart.series[0].remove();        }        chart.addSeries({            data: [100, 100, 100, 100, 29.9, 71.5, 106.4, 129.2, 144.0, 176.0, 135.6, 148.5]        });    } else if (x = 1) {        const series = chart.series[0];        if (series.data.length) {            chart.series[0].remove();        }        chart.addSeries({            data: [200, 200, 200, 200, 29.9, 71.5, 106.4, 129.2, 144.0, 176.0, 135.6, 148.5]        });    } else if (x = 2) {        const series = chart.series[0];        if (series.data.length) {            chart.series[0].remove();        }        chart.addSeries({            data: [200, 200, 200, 200]        });    }}</script>