jquery的validate使用

<script>
    //自定义校验规则
    $.validator.addMethod(
        //规则名称
        "isExit",
        function (value,element,params) {

            var isE=false;
            //value 输入的内容
            //element 被校验的元素对象
            //params 规则对应的参数值
            $.ajax({
                async:false,//同步
                url: "/isExit",
                type: "get",
                data: {"username": value},
                success: function (result) {

                    if (result == "true") {
                        isE=true;
                    }
                }
            })
            //返回false代表校验器不通过
            return isE;
        })
    $(document).ready(function () {
        //validate表单校验
        $("#user").validate({
            rules: {
                username:
                    {
                        required: true,
                        rangelength:[6,12],
                        isExit:true
                    },
                password: {
                    required: true,
                    minlength: 6,
                    maxlength: 12
                },
                rep: {
                    required: true,
                    equalTo: "#password"

                }
            },
            messages: {
                username: {
                    required: "用户名不能为空!",
                    rangelength:"长度为6~12",
                    isExit:"用户名已存在！"
                },
                password: {
                    required: "密码不能为空！",
                    minlength: "密码最小长度为6！",
                    maxlength: "密码最大长度为12！"
                },
                rep: {
                    required: "确认密码不能为空!",
                    equalTo:"两次输入的密码不一致！"

                }
            }

        })

    })

</script>