Return a return value from Perl to Javascript

Hello,

I have a form in which the user can enter a query in a query language.
The form is submitted to a perl script that checks if the syntax is OK
and if yes, execute the query and generates a html result page. If
the syntax is not OK, I want the client to display an error message,
in a small pop up window on top of the page from which the form was
submitted. The appearance of the pop up windows must be triggered if
the return value of the perl script is 1. Generating a pop up window
with javascript is easy, but how can I obtain the return value from
the perl script in Javascript ?
I considered the use of cookies, but in case a browser has disabled
them this won't work.
Any ideas?

Thanks.

Peter van der Kamp

PvdK