利用jQuery.Validate异步验证用户名是否存在（推荐）

<script type="text/JavaScript" src="../js/jQuery-1.3.2.min.js"></script><script type="text/javascript" src="../js/jquery.validate.min.js"></script><script type="text/javascript" src="../js/messages_cn.js"></script>

<form name="form1" id="form1" method="post" action=""><dl> <dt>用户名：</dt> <dd><input name="txtUserName" id="txtUserName" type="text" class="input1" /></dd></dl></form>

$(function() {//表单验证JS  $("#form1").validate({    //出错时添加的标签    errorElement: "span",    rules: {      txtUserName: {        required: true,        minlength: 3,        maxlength: 16,        remote: {          type: "post",          url: "/tools/ValidateUserName.ashx",          data: {            username: function() {              return $("#txtUserName").val();            }          },          dataType: "html",          dataFilter: function(data, type) {            if (data == "true")              return true;            else              return false;          }        }      }    },    success: function(label) {      //正确时的样式      label.text(" ").addClass("success");    },    messages: {      txtUserName: {        required: "请输入用户名，3-16个字符（字母、数字、下划线），注册后不能更改",        minlength: "用户名长度不能小于3个字符",        maxlength: "用户名长度不能大于16个字符",        remote: "用户名不可用"      }    }  });});

data: {  username: function() {  return $("#txtUserName").val();}