Mastering popup window using javascript

[Webiter]

At this test position there is a Subscribe facility that could be on a website page!

I am seeking to have the thanks.php page message present in a popup when a visitor fills out and submits the Subscribe Email.

I have included the following javascript on the subscribe.html page to help achieve this:

function popup_win(theURL,winName,winOptions) {
   win = window.open(theURL,winName,winOptions);
   win.focus();
 }

 function thankyou() {
   document.action = "    ";
   popup_win('   ','    ','resizable=yes,scrollbars=yes,width=180,height=180');
   document.target = "    ";
   document.submit();
 }

Could I get some help with the blanks in the thankyou function snippet...!