​x
 
<!DOCTYPE html>
<html>
<head>
<script>
function ChangeOpacity(x)
{
// 返回被选选项的文本
var opacity=x.options[x.selectedIndex].text;
var el=document.getElementById("p1");
if (el.style.opacity!==undefined)
  {el.style.opacity=opacity;}
else
  {alert("Your browser doesn't support this example!");}
}
</script>
</head>
<body>
​
<p id="p1">请从下面的例子中选择一个值，以改变此元素的不透明度。</p>
<select onchange="ChangeOpacity(this);" size="5">
  <option />0
  <option />0.2
  <option />0.5
  <option />0.8
  <option selected="selected" />1
</select>
​
</body>
</html>
​