var
   username = document.querySelect("#username"),
   pwd1 = document.querySelect("#password"),
   pwd2 = document.querySelect("password-2"),
   user_re = /^\w{3,10}/,
   pwd_re = /.{6,20}/;
   if (!user_re.test(username.value)) {
      alert("用户名必须是3-10位英文字母或数字");
      return false;
   } else if (!pwd_re.test(pwd1.value)) {
      alert("密码长度必须是6-20位");
      return false;
   } else if (pwd1.value != pwd2.value) {
      alert("两次密码必须一致");
      return false;
   }
   return true;
}