<select name="sel" id="sel">
<option>1</option>
<option>2</option>
</select>
<script>
var se=document.getElementById("sel");
se.onchange=new Function("alert('aaa');");
</script>
<option>1</option>
<option>2</option>
</select>
<script>
var se=document.getElementById("sel");
se.onchange=new Function("alert('aaa');");
</script>
var se=document.getElementById("sel");
se.onchange=a;
//or this:se.attachEvent("onchange",a)
function a(){
alert('aaa')
}
</script>