var pop = null;

function popdown() { 
  if (pop && !pop.closed) pop.close();
}

function popup(obj,w,h) {
  var url = (obj.getAttribute) ? obj.getAttribute('href') : obj.href;
  if (!url) return true;
  w = (w) ? w += 20 : 250;  // 250px*350px ist die Standardgröße
  h = (h) ? h += 25 : 350;
  var args = 'width='+w+',height='+h+',resizable';
  popdown();
  pop = window.open(url,'',args);
  return (pop) ? false : true;
}

function zeig(obj,pic) {
  obj.setAttribute('src',pic);
}

// window.onfocus = popdown;
window.onunload = popdown;