// <a href="dokument.html" onclick="return popup(this,123,456)" title="..."
// oder
// <a href="image.jpg" onclick="return popup(this)" title="..."

var pop = null;

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

function popup(obj,w,h,addargs) {
  var url1 = (obj.getAttribute) ? obj.getAttribute('href') : obj.href;
  if (!url1) return true;
  w = (w) ? w += 50 : 150;  // 150px*150px is the default size
  h = (h) ? h += 25 : 150;
  if (!addargs) addargs = 'resizable=yes,scrollbars=yes,status=no,toolbar=no,directories=no,menubar=no,location=no';
  var args = 'width='+w+',height='+h+','+addargs+'';
  popdown();
  pop = window.open(url1,'',args);
  return (pop) ? false : true;
}

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

// addargs:
// resizable=yes, scrollbars=yes, status=no, toolbar=no, directories=no, menubar=no, location=no