Execute Javascript after *.jspx page rendered

Question

I have a page with controls and a subform with a servlet, rendering a jasper report:
               <af:panelFormLayout id="pfl1" partialTriggers="cbReportHTML">
                <af:subform id="sfRep">
                  <jsp:include page="/jasperservlet" flush="true"/>
                </af:subform>
              </af:panelFormLayout>
I want the page to be rendered before the subform (so that user can see controls on page before the report).
"/jasperservlet" generates the report in about half a minute.
I want to have a JavaScript that runs after the page is rendered (and the user sees the controls) and then it starts to generate report.
I tried to put a frame with such javascript, but the javascript is executed before user can see controls.
How can it be done?

Answer 1

Thank you for your answers.
Yes, I'm trying to execute javascript code on the child page, the modal one.
Basically, there's a button on my parent page which opens the modal page. The modal page has buttons Cancel, Delete and Save. Clicking Save button submits the changes and if there are errors, errors are shown and we stay on the modal page.
My modal pages are all of fixed dimensions and if there are errors, I have to adjust the other regions (adjust their height, add a scrollbar, etc) in order to show everything in the modal page.
I have written a function that does exactly that, but I have to execute the function after the page is loaded and the regions are shown. But, if I execute it using onload attribute, or setting a dynamic action which fires on page load, the function gets executed during the submit, before the regions are shown.
I hope I have managed to clear up the problem.
As always, thank you.