[jQuery] validate a form using jsVal script

[JP]

In an $.ajax option  beforsend, I want to call a function to validate
a form using jsVal script

(jsVal  is here:  http://jsval.fantastic-bits.de/  The home page shows
examples)

I tried the following:
...
         $.ajax({
                 beforeSend: showRequest,
...

        function showRequest(){//alert('showRequest');
                var objForm = document.forms["contactForm"];
                validateStandard(objForm, 'error');
        }

The alert will show but,  validateStandard()  is not processed.
jquery ignores this and proceeds ahead with submittal, which is
successful.

How can I correctly use a third party script like jsval to validate
the form before it is submitted by jquery ajax ?