function CheckTrip() {
  number = document.getElementById('txtNumber');
  lastname = document.getElementById('txtLastName');

  if (number.value.length < 1) {
    alert('Please enter reservation number');
    return false;
  }

  if (lastname.value.length < 1) {
    alert('Please enter last name');
    return false;
  }
  

  url = "https://www.checkmytrip.com/CMTSERVLET?R=" + number.value + '\&L=GB&N=' + lastname.value;
  newWindow = window.open(url, "mywindow", "location=no,status=no,scrollbars=yes,width=700,height=500,resizable=yes,directories=no");
}