用js做登录的用户名判定

<script type="text/javascript" language="javascript" src="JS/jquery.js"></script>
    <script language="javascript" type="text/javascript">
      $(document).ready(function() {
             $("#userName").blur(function(){
     $.ajax({
      type:'POST',
      url:'servlet/valUserNameServlet',
      data:'userName='+$("#userName").val(),
      beforeSend: function(){
       $("#progress").html("<img src='image/search.gif' alt='' />")
       },
       complete:function (XMLHttpRequest, textStatus){
        $("#progress").html("");
       },
      success:function(msg){
       if(msg=='true'){
        $("#userNameInfo").html("用户名可用");
       }else{
        $("#userNameInfo").html("<span style='color:red'>用户名已占用</span>");
       }
      }
       });
            });
     });

</script>