javascript - 取值，用输出更新字段

Question

我的目标:是通过我的函数更新字段获取选定值并使用函数输出值运行它。

问题:当我从列表中选择值时，它不会触发函数，也不会更新字段。

感谢您的帮助。

HTML

<form id="someform">
<select id="sample" onChange="dIIN()">
<option>12</option>
<option>14</option>
<option>16</option>
<option>18</option>
<option>20</option>
<option>22</option>
<option>24</option>
<option>27</option>
<option>30</option>
<option>32</option>
</select> 
</form>

<tr>
<td>Quantity to be dredged</td>
<td><input type="number" value="450000" class="" id="quantity-dredged" ></input></td>
</tr>

JavaScript

var dIIN = function() {
  var dredgeSize = document.getElementById('sample');
  var foo = 0;
  if (dredgeSize <= 12) {
    foo = 36;
  } else if (dredgeSize <= 14) {
    foo = 42;
  } else if (dredgeSize <= 16) {
    foo = 44;
  } else if (dredgeSize <= 18) {
    foo = 48;
  } else if (dredgeSize <= 20) {
    foo = 60;
  } else if (dredgeSize <= 22) {
    foo = 62;
  } else if (dredgeSize <= 24) {
    foo = 62;
  } else if (dredgeSize <= 26) {
    foo = 68;
  } else if (dredgeSize <= 28) {
    foo = 68;
  } else if (dredgeSize <= 30) {
    foo = 74;
  }
  document.getElementById('quantity-dredged').value = foo;
};

这是一个 codePen example

Answer 1

改变行:

var dredgeSize = document.getElementById('sample');

到:

var dredgeSize = document.getElementById('sample').value;

Demo