The event system within JavaScript is an important part of the language. JavaScript was designed to respond to events in the browser and events caused by users. A website may need to respond to the click of a user, or an AJAX response from a server. With the language, you can attach functions called event handlers to listen for events from certain elements in the page and the browser.

In the Dojo framework, events are listened to using the dojo/on module. When assigning an event listener, the module function call returns an object that lets you discontinue listening by calling the object's remove() method. Also, dojo/on has a once() method that fires the event once, when the event occurs, then automatically removes the event.