Comment Re: Citation Needed (Score 1) 354
If you want to you could have whatever validation (or any) script you use on the server be sent to the client to be run before they submit the data. You still have server side sanity checking and you get client side for "free".
I assume the sell is mainly part of being able to seamlessly share data via JSON (without extra parsers) and working with one language all the time. That's the main "cool" factor for me. I don't have to switch "modes" and think Ruby/.NET/PHP when working on the backend and then switch to thinking "JavaScript" on the front.