<html>
<body>
<p>点击按钮创建 OPTGROUP 元素。</p>
<button onclick="myFunction()">尝试一下</button>
<select id="mySelect" size="6">
<option>BMW
</option><option>Mercedes
</option><option>Ford
</option><option>Volvo
</option><option>Toyota
</option></select>
<script>
function myFunction()
{
var x = document.getElementById("mySelect");
var y = document.createElement("OPTGROUP");
y.setAttribute("label", "SwedishCars");
y.appendChild(x.options[3])
x.insertBefore(y,x.options[3]);
}
</script>
</body>
</html>