​x
 
<html>
<head>
<script type="text/javascript">
function alertOptionId()
  {
  var x=document.getElementById("mySelect").selectedIndex;
  alert(document.getElementsByTagName("option")[x].id);
  }
</script>
</head>
<body>
​
<form>
Select your favorite fruit:
<select id="mySelect">
<option id="apple">Apple</option>
<option id="orange">Orange</option>
<option id="pineapple">Pineapple</option>
<option id="banana">Banana</option>
</select>
<br /><br />
<input type="button" onclick="alertOptionId()" value="Alert id">
</form>
</body>
</html>
​