javascript - Google Charts - Google Visualization arraytoDataTable 无法识别数值，除非 "treated"

Question

看看this JsFiddle .

我正在尝试从表单字段导入一个值，将其分配给一个变量，然后将其传递给 google.visualization.arrayToDataTable。

但在这两种情况下，甚至强制将 type: 'number' 分配为 in this answer我总是会遇到某种错误:

案例 1:

<form name="myForm">
<input type="number" name="tot_btc" id="tot_btc" value="250">

var points  = document.forms.myForm.tot_btc.value;

var data = google.visualization.arrayToDataTable([
          ['Name', {label: 'Donuts eaten', type: 'number'}],
        //['Name', 'Donuts eaten'],
          ['Michael' , points],
          ['Elisa', 7],
          ['Robert', 3],
          ['John', 2],
          ['Jessica', 6],
          ['Aaron', 1],
          ['Margareth', 8]
        ]);

我遇到这种错误:

如您所见，已确认该值，但未绘制图表:它是空白的。

---

案例 2:

<form name="myForm">
<input type="number" name="tot_btc" id="tot_btc" value="250">

        var data = google.visualization.arrayToDataTable([
        //['Name', {label: 'Donuts eaten', type: 'number'}],
          ['Name', 'Donuts eaten'],
          ['Michael' , points],
          ['Elisa', 7],
          ['Robert', 3],
          ['John', 2],
          ['Jessica', 6],
          ['Aaron', 1],
          ['Margareth', 8]
        ]);

我删除了type: 'number' 赋值，结果甚至没有识别出数字。

---

案例 3:

现在，看看这个:

但是 如果我从变量中取出数字并执行任何简单的数学运算，瞧!数字被识别并且图表被绘制..即使没有强制类型:'number'识别:

谁能解释一下？

谢谢

Answer 1

虽然你设置了<input>作为型号，
value属性总是会返回一个字符串，这里...

    var points  = document.forms.myForm.tot_btc.value;

来自 MDN - HTMLInputElement - Properties ，可以看到属性type = string...

value string: Returns / Sets the current value of the control.

---

必须转换为实际数字，
在将值提供给 arrayToDataTable 之前

这就是为什么对变量执行数学运算会导致它起作用的原因。

要更正，将值解析为数字，
使用 parseInt或 parseFloat ...

    var points  = parseFloat(document.forms.myForm.tot_btc.value);

请参阅以下工作片段...

      google.charts.load('current', {'packages':['corechart', 'controls']});
      google.charts.setOnLoadCallback(drawStuff);

      function drawStuff() {

        var dashboard = new google.visualization.Dashboard(
          document.getElementById('programmatic_dashboard_div'));

        // We omit "var" so that programmaticSlider is visible to changeRange.
        var programmaticSlider = new google.visualization.ControlWrapper({
          'controlType': 'NumberRangeFilter',
          'containerId': 'programmatic_control_div',
          'options': {
            'filterColumnLabel': 'Donuts eaten',
            'ui': {'labelStacking': 'vertical'}
          }
        });
//        var points  = document.forms["myForm"]["points"].value;
        var points  = parseFloat(document.forms.myForm.tot_btc.value);
        var cazzo = 81;

        var programmaticChart  = new google.visualization.ChartWrapper({
          'chartType': 'PieChart',
          'containerId': 'programmatic_chart_div',
          'options': {
            'width': 300,
            'height': 300,
            'legend': 'none',
            'chartArea': {'left': 15, 'top': 15, 'right': 0, 'bottom': 0},
            'pieSliceText': 'value'
          }
        });

        var data = google.visualization.arrayToDataTable([
       // ['Name', {label: 'Donuts eaten', type: 'number'}],
          ['Name', 'Donuts eaten'],
          ['Michael' , points],
          ['Elisa', 7],
          ['Robert', 3],
          ['John', 2],
          ['Jessica', 6],
          ['Aaron', 1],
          ['Margareth', 8]
        ]);

        dashboard.bind(programmaticSlider, programmaticChart);
        dashboard.draw(data);

        changeRange = function() {
          programmaticSlider.setState({'lowValue': 2, 'highValue': 5});
          programmaticSlider.draw();
        };

        changeOptions = function() {
          programmaticChart.setOption('is3D', true);
          programmaticChart.draw();
        };
      }

<script type="text/javascript" src="https://www.gstatic.com/charts/loader.js"></script>
<div id="programmatic_dashboard_div" style="border: 1px solid #ccc">
  <table class="columns">
    <tr>
      <td>
       <div id="programmatic_control_div" style="padding-left: 2em; min-width: 250px"></div>
       <form name="myForm">
       <input type="number" name="tot_btc" id="tot_btc" value="2">
       <input type="range" onmousedown="return showInput()" onmouseup="return showInput()" name="points" min="0" max="10">
       </form>
        <div>
          <button style="margin: 1em 1em 1em 2em" onclick="changeRange();">
            Select range [2, 5]
          </button><br />
          <button style="margin: 1em 1em 1em 2em" onclick="changeOptions();">
            Make the pie chart 3D
          </button>
        </div>
        <script type="text/javascript">
          function changeRange() {
            programmaticSlider.setState({'lowValue': 2, 'highValue': 5});
            programmaticSlider.draw();
          }

          function changeOptions() {
            programmaticChart.setOption('is3D', true);
            programmaticChart.draw();
          }
        </script>
      </td>
      <td>
        <div id="programmatic_chart_div"></div>
      </td>
    </tr>
  </table>
</div>