function addLoadListener(fn) {
  if (typeof window.addEventListener != 'undefined') {
    window.addEventListener('load', fn, false);
  } else if (typeof document.addEventListener != 'undefined') {
    document.addEventListener('load', fn, false);
  } else if (typeof window.attachEvent != 'undefined') {
    window.attachEvent('onload', fn);
  } else {
    var oldfn = window.onload;
    if (typeof window.onload != 'function') {
      window.onload = fn;
    } else {
      window.onload = function() {
        oldfn();
        fn();
      };
    }
  }
}

function createPopup() {
	var status = false;
	var urlext;
	if (document.getElementById('invalidQuantity')) {
		status = true;
		urlext = 'invalidQuantity';
	} else if (document.getElementById('emptyForm')) {
		status = true;
		urlext = 'emptyForm';
	}
	if (status) {
		winOpen('popup', 'pop_up.php?w='+urlext, 350, 150);
	}
}

function winOpen(name, url, w, h) {
	wleft = (screen.width - w) / 2;
	wtop = (screen.height - h) / 2;
	var win = window.open(url,
		name,
		'width=' + w + ', height=' + h + ', ' +
		'left=' + wleft + ', top=' + wtop + ', ' +
		'resizable=no, scrollbars=no');
	win.focus();
}

addLoadListener(createPopup);