Your Ext JS application makes use of events to handle user interaction, but it is also easy to have your classes communicate with each other via events.
Ext JS is very mature in the way it handles events, as it's something that's been at the core of the framework since the beginning. It uses an observer pattern to allow your classes to publish events and others to subscribe to those events. Your subscribing class will have its logic triggered as soon as the publishing class fires the event. This paradigm is asynchronous and modular.
As we covered in Chapter 2, Mastering the Framework's Building Blocks, the event-driven logic in Ext JS is handled by the Ext.mixin.Observable class.