js insertBefore

     <select id="city" size="4" style="width:50px">
         <option id="hn">湖南</option>
         <option id="hb">湖北</option>
     </select>
       <script type="text/javascript">
           /*创建"新元素"，插入到"湖南"元素之前
           var newOptionElement = document.createElement("option");
           newOptionElement.setAttribute("id","new");
           newOptionElement.innerHTML = "新元素";
           var cityElement = document.getElementById("city");
           var hnElement = document.getElementById("hn");
           cityElement.insertBefore(newOptionElement,hnElement);　　//新元素
         */
           //创建"新元素"，插入到"湖南"元素之后
           var newOptionElement = document.createElement("option");
           newOptionElement.setAttribute("id","new");
           newOptionElement.innerHTML = "新元素";
           var cityElement = document.getElementById("city");
           var hnElement = document.getElementById("hn");        

             //兄弟节点  nextSibling
             cityElement.insertBefore(newOptionElement,hnElement.nextSibling);
      </script>