Dojo: The Definitive Guide

Event Listeners

Direct communication channels are constructed by explicitly chaining together functions and/or DOM events so that when one executes, another is automatically invoked afterward. For example, each time an object changes via a "setter" method, you may want to automatically trigger a change in the application's visual interface. Or, perhaps each time one object changes, you might want to automatically update a derived property on another object. The possibilities are endless.

The two primary methods involved in a direct communication scheme are dojo.connect and dojo.disconnect. In short, you use dojo.connect to chain together a series of events. Each call to dojo.connect returns a handle that you should keep and explicitly pass to dojo.disconnect whenever you are ready to dispose of the connection. Conveniently, all handles are disconnected automatically when the page unloads, but manual management of the handles may be necessary for preventing memory leaks in long-running applications that invoke a lot of connections that are used temporarily. (This is particularly the case on IE.) Coming up is the API that was introduced in Chapter 1.

Warning

Don't ever connect anything until after the page is loaded. Trying to use dojo.connect before the page is loaded is a very common mistake and can cause you to sink a lot of time into trying to debug something that isn't very easy to track down the first time you run into it. You should always set up your connections within the function ...