colorbox check parent element exist

Question

Hi,

i am using colorbox to open a window that appears a grid with categories. After select the check boxes i draw the categories at parent window.So far so good.

My problem is that before draw i check if the category exist in parent window but its not working

if($('#cat-2', window.parent.document).length==0)
  $('#categories', window.parent.document).append(newdata);

Am i missing something.