var win;
function popup(theURL,winName,features) {
  if (win && win.open && !win.closed) win.close();
  win = window.open(theURL,winName,'toolbar=no,location=no,status=no,menubar=no,' + features);
}

function popupCenter(theURL,winName,features,w,h) {
  if (win && win.open && !win.closed) win.close();
  var left = (screen.width/2)-(w/2);
  var top = (screen.height/2)-(h/2);

  win = window.open(theURL,winName,'toolbar=no,location=no,status=no,menubar=no,' + features + ',width='+w+', height='+h+', top='+top+', left='+left);
}