var fenster

function openWindow (url,width,height,screenX,screenY,menubar) {
  var optionen = "width=" + width + ",height=" + height + ",screenX=" + screenX + ",screenY=" + screenY + ",menubar=" + menubar
  if (!fenster) {
    fenster = window.open(url, "neu", optionen)
  } else {
    fenster.close()
    fenster = window.open(url, "neu", optionen)
  }
}