js insertBefore

    <select id="city" size="4" style="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>