Document Object Model in JavaScript
The document object model, or DOM, refers to the Web page components, or objects, that you can access and manipulate by using JavaScript. Examples of objects that you can work with in JavaScript include the window that a Web page appears in, the Web page itself, embedded images and text, and much much more.
Because JavaScript is object-based, when you program in JavaScript you get to take advantage of a predefined object model. Ojbect-base programming laguages package, or encapsulate, date and functionality into useful units called ojbects. (Collectively, the objects that you work with in an object-based programming language are called the object model.) Encapsulation is a good thing, because it hides nitty-gritty programming details -- allowing you the programmer, to write code with least amount of hassle possible.
The DOM performs task by describing
* All the objects that go into making up a Web page, such as forms, links, images, buttons, and text.
* The descriptive properties associated with each of the DOM objects. For example, image object can be associated with specific properties describing its height and width.
* The behaviors, or methods, associated with each of the DOM objects. For example, the window object supports a method called alert() that allows you to display an alert message on a Web page.
* The special built-in methods, called event handlers, associated with automatic and user-initiated events. For example, loading a Web page into a browser is considered an event; so is clicking a button. The event handler that you use to trigger some JavaScript code when these events occur are called onLoad and onClick, respectively.
Most of the objects that you work with in JavaScript fall into the following four categories:
1) Objects defined by using HTML tags. This includes documents, links, applets, text fields, windows, and so on.
2) Objects defined automatically by Web browsers. One example is the navigator object, which, despite its name, holds configuration and version information about whichever browser is currently in use, even if that browser happens to be IE.
3) Objects that are built into JavaScript, such as Date and Number.
4) Objects you yourself have created by using the JavaScript new operator.
posted by Larry Zhou @ 11:40 PM
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