A very common problem new developers face when they start using Knockout is how to communicate between viewmodels without establishing a single hierarchy with a master viewmodel or any other form of direct reference between viewmodel objects. These kind of hard dependencies are generally considered bad practice, but the need to send messages between different viewmodels is unavoidable.

The publish-subscribe (pub/sub) pattern is a popular solution to this problem. Durandal offers you a simple pub/sub implementation via the Events module. There are two ways in which you can use the events system: with the events included on the durandal/app object by default or by adding events to your own objects.