Learning JavaScript

Chapter 6. Catching Events

Events let you know when a user is doing something or when a page has loaded. Catching and handling events lets your code do the right thing at the right time, serving the users of your programs.

Regardless of why they happen or how they’re implemented, events in JavaScript are associated with objects and are not intrinsic to the language itself. Typically, when working with browsers, events are related to the DOM implemented in each browser.

There is a default behavior associated with each event, but events can be used to modify functionality or add additional functionality. Extending the event behavior can be managed within the (X)HTML tag for the object, or in a separate JavaScript code block or file.

The events themselves are fairly intuitive. The W3C (World Wide Web Consortium) categorizes events into three distinct areas: user interface (mouse, keyboard), logical (result of a process), and mutation (action that modifies a document). The basic events, affected objects, and descriptions are listed in Table 6-1.

Table 6-1. Events and affected objects

Event	Description	Object(s)
abort	When image is prevented from loading	An image element
blur,focus	When object loses or receives focus	Applicable to window and form elements
change	When selection changes	Applicable to form elements where value changes and after element loses focus
click, doubleclick (dblclick)	Clicking or double clicking (two clicks in rapid succession) with mouse	Most page elements
contextmenu	Clicking ...