var openWindow;

function openCarClassWindow(klasse) {
  if(openWindow==undefined)
  {
    openWindow=window.open("klasse/"+klasse+".html","","width=600, height=800, left=150, top=150, scrollbars=yes, status=yes");
    prereserve=0;
    car_class=klasse;
    PreReserve();
  } else {
    openWindow.focus();  
  }
}

function PreReserve() {
  if(openWindow.closed)
  { 
    // try to find out if the pre-reserve button is hit
    if (prereserve==1) {
      window.location='reserveer_auto_stap2.php?stap=2&klasse='+car_class;
    }
    openWindow=undefined;
  } else {
   setTimeout('PreReserve()', 100);
  }
}