JQuery動态添加input的值

<input type="text"  οnchange="change()" name="username" value="${actionBean.map.username }" class="k-textbox easyui-validatebox" validType="maxLength[15]" required="true">      

<script type="text/javascript">

 function change(){
var map_pkid=$("#map_pkid").val();
    if($("#pkid").val()==""){
    $("#pkid").attr("value",map_pkid);
      }  
   }
 </script>