【JS】js获得下拉列表选中项的值和id

 function tijiao(){
         var elem = document.getElementById("dish_sort");
         var index=elem.selectedIndex;
         alert(elem.options[index].value);
         alert(elem.options[index].id);
     }

 <td>菜品分类：</td><td><select name="dish_sort" id="dish_sort">
             <c:forEach var="a" items="${list}">
                 <option id="${a.id}" value="${a.sort}">${a.sort}</option>
             </c:forEach>
             </select></td>