'is' - A lightweight JavaScript-library for validations and checks

There are large web-frameworks such as dojo and extJS, which even at their bare essential introduce a great deal of excess code when only a tiny subsets of function's are needed. As such the rule of thumb is to not include more than one library.

I was interested in a very small library which provides a good starting point for any new script, which barely  introduces any overhead, and is easy to manage.

Here is the work in progress. You can download or fork it on github.
It's primary goal is to remain lightweight (~3kB) and useful.

Here are some code examples: