var popUpWin=0;
function open_form(url) {
         var top=0;
         var left=0;
         var width=998;
         var height=720;
           if(popUpWin)  {
              if(!popUpWin.closed) popUpWin.close();
           }
         popUpWin = window.open(url, 'Stellenbewerbung', 'toolbar=no,location=no,directories=no,status=no,menubar=no,scrollbars=yes,resizable=yes,width='+width+',height='+height+',left='+left+',top='+top+',screenX='+left+',screenY='+top);
}