var pop = null;

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

function popauf(obj,b,h) {
  var url = (obj.getAttribute) ? obj.getAttribute('href') : obj.href;
  if (!url) return true;
  b = (b) ? b += 20 : 400;  // 400px*400px breite mal höhe
  h = (h) ? h += 25 : 400;
  var args = 'width='+b+',height='+h+',resizable';
  popzu();
  pop = window.open(url,'',args);
  return (pop) ? false : true;
}

window.onunload = popzu;
window.onfocus = popzu;