With the right abstractions the code for validating on the client and for validating on the server can be identical. For example take a look at Luna/Lunascript.

With the right abstractions the code for validating on the client and for validating on the server can be identical. For example take a look at Luna/Lunascript. This is not easy by just using Node, and it's not necessary that the language you use is Javascript. A better approach IMO is that you have a language X that is nicer than Javascript, and compiles both to server side code and client side Javascript. For the case of validation here is a hypothetical language (ignore the bad regex): <form action="/foo/bar"> <input type="text" name="email" /> <%= if not email ~ "[a-z]+@[a-z]+.[a-z]+": invalid("Email is not valid") %> <submit> </form> From this code you could generate real time JS validation and server side validation.