Anything done in Javasript in a browser can and will be subverted by a malicious user, or will break on certain browsers, or will simply not be executed when users have disabled Javascript, or will get blocked by content filters, or ...

Sure, use Javascript if you want to be nice and friendly and give instant feedback on errors, but TEST TEST TEST so that it doesn't break hideously in browsers other than the one you habitually use. And even then, you must also validate the data on the server, lest you have a nasty user like me trying to break your data. Of course, using Javascript means you need to do at least twice as much work - you need to write and test and maintain Javascript as well as writing and testing and maintaining perl. Does your employer really want you to do that?