1.2. Observer Pattern in JavaScript

The observer pattern is defined as a way of creating a one-to-many relationship among objects in which change notifications are automatically dispatched to listening objects. The common terms used in describing the observer pattern include designating a "publisher" and a "subscriber." As the publisher is updated, each of the subscribing objects has an opportunity to respond to the change.

The following is a quick primer on how the observer pattern is implemented in the ASP.NET 4 AJAX Framework. Consider a page that allows you to update a person's last name, as shown in Figure 6.