This differs from example Ruby on Rails where validators instead have the option.I find it quite common that you want to have constraints on an optional attribute.
The project can be found on Git Hub where you can also find our issue tracker.
There is also a Travis project used for testing, a Coveralls project used to code coverage as well as the annotated source.
You can tell to use any A compatible promise implemention like this: There are already many validation libraries out there today but most of them are very tightly coupled to a language or framework.
The goal of is to provide a cross framework and cross language way of validating data.
The validation constraints can be declared in JSON and shared between clients and the server. One thing that is a bit unorthodox is that most validators will consider undefined values (,) valid values.