利用jQuery.validate异步验证用户名是否存在

转：http://www.cnblogs.com/linzheng/archive/2010/10/14/1851781.html

HTML头部引用：

<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>

HTML内容（部分）：

<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>

JS代码部分：

$(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"
            }
        }

});
});

应注意的地方：

data: {
   username: function() {
   return $("#txtUserName").val();
}
有返回值，如果直接写“data: {username: $("#txtUserName").val();}”，这样是获取不到值的。