function preview() {
  var url = window.location.href;
  if (url.indexOf('?')==-1) {
    url = url + '?previewMode=1';
  } else {
    url = url + '&previewMode=1';
  }
  window.open(url, 'preview', 'height=750,location=no,menubar=no,resizable=yes,scrollbars=yes,status=no,toolbar=no,width=1000');
}