HTML DOM index 属性
Option 对象参考手册定义和用法
index 属性可返回下拉列表中选项的索引位置。
语法
optionObject.index
实例
本例可返回下拉列表中所选的选项的索引位置：
<<html>
<head>
<script type="text/javascript">
function alertIndex()
{
var x=document.getElementById("mySelect").selectedIndex;
var y=document.getElementsByTagName("option");
alert(y[x].text + " has the index of: " + y[x].index);
}
</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="alertIndex()"
value="Show index of the chosen fruit">
</form>
</body>
</html>