selectedIndex 属性

selectedIndex 属性可设置或返回下拉列表中被选选项的索引号。

注释：若允许多重选择，则仅会返回第一个被选选项的索引号。

语法

selectObject.selectedIndex=number

实例

下面的例子可提示出被选选项的索引号：

<html>
<head>
<script type="text/javascript">
function getIndex()
  {
  var x=document.getElementById("mySelect")
  alert(x.selectedIndex)
  }
</script>
</head>
<body>

<form>
Select your favorite fruit:
<select id="mySelect">
  <option>Apple</option>
  <option>Orange</option>
  <option>Pineapple</option>
  <option>Banana</option>
</select>
<br /><br />
<input type="button" onclick="getIndex()"
value="Alert index of selected option">
</form>

</body>
</html>

<html>
<head>
<script type="text/javascript">
function insertBeforeSelected()
  {
  var x=document.getElementById("mySelect");
  if (x.selectedIndex>=0)
    {
    var y=document.createElement('option');
    y.text='Kiwi';
    var sel=x.options[x.selectedIndex];  
    try
      {
      x.add(y,sel); // standards compliant
      }
    catch(ex)
      {
      x.add(y,x.selectedIndex); // IE only
      }
    }
  }
</script>
</head>
<body>

<form>
<select id="mySelect">
  <option>Apple</option>
  <option>Pear</option>
  <option>Banana</option>
  <option>Orange</option>
</select>
<input type="button" onclick="insertBeforeSelected()" value="Insert option before selected" />
</form>

</body>
</html>