<html>
<body>
<h3>访问 OPTGROUP 元素</h3>
<select size="4">
<optgroup id="myOptgroup" label="Swedish Cars">
<option value="volvo">Volvo</option>
<option value="saab">Saab</option>
<option value="koenigsegg">Koenigsegg</option>
</optgroup>
</select>
<p>点击按钮获取选项组的标签/描述。</p>
<p id="demo"></p>
<button onclick="myFunction()">尝试一下</button>
<script>
function myFunction()
{
var x = document.getElementById("myOptgroup").label;
document.getElementById("demo").innerHTML = x;
}
</script>
</body>
</html>