​x
 
<!DOCTYPE html>
<html>
<body>
​
<p>单击按钮可创建一个 OPTGROUP 元素。</p>
​
<button onclick="myFunction()">试一试</button>
​
<select id="mySelect" size="6">
  <option>BMW
  <option>Mercedes
  <option>Ford
  <option>Volvo
  <option>Toyota
</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>
​