<html>
<body>
<select size="6">
<option value="BMW">BMW</option>
<option value="Mercedes">Mercedes</option>
<optgroup id="myOptgroup" label="Swedish Cars">
<option value="volvo">Volvo</option>
<option value="saab">Saab</option>
<option value="koenigsegg">Koenigsegg</option>
</optgroup>
</select>
<p>点击按钮改变选项组的 label 属性的值。</p>
<button onclick="myFunction()">尝试一下</button>
<script>
function myFunction()
{
document.getElementById("myOptgroup").label="A Random Car Selection";
}
</script>
</body>
</html>