function ischeck(){

var postcode = document.getElementById("postcode").value;

            if (postcode != "") {   //邮政编码判断

                var pattern = /^[0-9]{6}$/;

                flag = pattern.test(postcode);

                if (!flag) {

                    alert("非法的邮政编码！")

                    document.getElementById("postcode").focus();

                    return false;

                }

            }

}