<html>
<head>
<script type="text/javascript">
function getLength()
{
alert(document.getElementById("mySelect").length)
}
</script>
</head>
<body>
<form>
<select id="mySelect">
<option>苹果</option>
<option>桃子</option>
<option>香蕉</option>
<option>桔子</option>
</select>
<input type="button" onclick="getLength()" value="在这个列表中，有多少选项？">
</form>
</body>
</html>