I looked at the code, and what this does is to make calls to a web api on the errorjs.com domain.

It sets a key using:

http://rastajs.errorjs.com/set/yourkey/yourvalue

And retrieves it using:

http://rastajs.errorjs.com/get/yourkey

It also adds a timestamp, and allows for a callback. Perhaps it should be clarified that this relies on making a web call to their server (even if that is the only way this could possibly be done).