I would never rely on Javascript completely for form validation anyway since it can easily be bypassed. I'm not saying it shouldn't be done since it can save you a trip to the server is the user is playing nice.
To help out with the problem, there are
Data::FormValidator and
CGI::FormBuilder. The later even helps you do validation in both JS and Perl.
More people are killed every year by pigs than by sharks, which shows you how good we are at evaluating risk. -- Bruce Schneier