Unlike the DOM events that web programmers normally associate with the word "event", Dojo takes a broad view of events. The tools in dojo.event.* allow developers to treat any function call (DOM event or otherwise) as an event that can be listened to. Using Dojo, code can register to "hear" about any action through a uniform API.

Events are essential for Dojo based applications as they drive the user interface, result in AJAX requests, and allow widgets to interact with each other. In a sense events are the glue that ties an application together. Cross browser event handling code can difficult to write from scratch as there are many ways in JavaScript of handling events and each browser has its own quirks and issues.

Dojo abstracts the JavaScript event system in the dojo.event module and provides a few options for handling events which include simple event handlers, event listeners using before, after, and around advice, and topics. The Dojo event APIs are not mutually exclusive; in many cases you will use a combination of the APIs depending on your use cases.

In this chapter we'll show you:

• how to use these tools
• what makes them completely different from other JavaScript event systems you may have used
• why you'll never start writing JavaScript without dojo.event.connect() again.