Perl
----
use Sajax;

sub populate {
    my ($course) = @_;
    return "You selected $course";
}

Sajax::rs_init();
Sajax::rs_register("populate", \&populate);

...


JS outputed by Perl
-------------------

function do_populate() {
    x_populate(selectCourseDept.value, do_populate_cb);
}

function do_populate_cb(feedback) {
    feedback_field.innerText = feedback;
} 

HTML outputed by Perl
---------------------
...
<p>
<SELECT NAME="selectCourseDept" onChange="do_populate(); return false;">
...
</SELECT>
</p>
<p>You selected: <span id="feedback_field"></span></p>
...