from Hacker News

Gedi is an interface to your model that lets you bind events to track changes in the model. Gedi will also track the dirty state of your model.

Combined with gel (https://github.com/gaffa-tape/gel) gedi is extremely powerful, allowing expression base callbacks that will evaluate when any reference to the model is changed.

Some examples of usage are in the tests: http://github.korynunn.com/gedi/test.html