javascript 循环listbox中的值

<script language="javascript">
function ChangeCag()
{
 
 alert("ddd");
}
</script>

<select name="select1" size="5" multiple="multiple" id="select1">

         <option value="1" οndblclick="return ChangeCag();">aaa</option>
        

         <option value="2" οndblclick="javascript:ChangeCag()">ee</option>
        

         <option value="3" οndblclick="javascript:ChangeCag()">ee</option>
        

         <option value="4" οndblclick="javascript:ChangeCag()">qq</option>
        

         <option value="5" οndblclick="javascript:ChangeCag()">ws</option>
        

         <option value="6" οndblclick="javascript:ChangeCag()">erer</option>
        

 

</select>