Popup Child window content not rendering

I need to display some message to user untill it is refreshes content from database. i decided to open one  modalwindow which will display Refreshing... message to user.

i am putting following code in a function and once tasks completes i am closing that window but i am getting blank window. how i can render popup content

myfunction(){

var w=new Window();

w.content="Refreshing";

w.show();

return w;

}

main()

{

var w=myfunction();

dowork();

w.close();

}

F a i r L i g h t