VanadiumJS

Vanadium - Unobtrusive, Declarative, Server-side Technology Agnostic,
Ajax Enabled, Server-side Aware, Client-side Validation

Vanadium is JavaScript validation toolkit that makes client-side validation easy.
Here's a rundown of the functionality:

* Validation rules are applied to HTML elements by adding special markup classes. E.g. adding ':required' to element's classes
makes the element being validated against provided value
* Instead of markup, one can use external definition provided as json structure.
* It is Ajax enabled in that sense one can declare particular field being validated by the result of the server response.
E.g. adding ':ajax;/path_on_server/user_exists.json' to element's classes will cause any change to value of that element being
sent to server as request ....