var pop = null;

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

function popup(obj,w,h,d,m,r) {
  var url = (obj.getAttribute) ? obj.getAttribute('href') : obj.href;
  if (!url) return true;
  w = (w) ? w += 20 : 150;  // 150px*150px is the default size
  h = (h) ? h += 25 : 150;
  var args = 'width='+w+',height='+h+',resizable=0,scrollbars=1,directories='+d+',menubar='+m+',resizable='+r+'';
  popdown();
  pop = window.open(url,'',args);
  return (pop) ? false : true;
}

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