7.DOM简介.doc

DOM介绍 本文从概念上对DOM进行介绍：它是什么，如何为HTML和XML文本提供相应的结构，如何对DOM进行存取，这个API如何表示基准信息并举例说明。 DOM为何物? The Document Object Model is an API for HTML and XML documents. It does two things for web developers: it provides a structural representation of the document, and it defines the way that that structure is to be accessed from script, allowing you to get at the web page as a structured group of nodes, which we will discuss shortly. Essentially, it connects web pages to scripts or programming languages. Note that the DOM is not a particular application, product, or proprietary ordering of web pages. Rather, it is an API, an interface that vendors must implement if they are to be conformant with the W3C DOM standard. Every browser vendor that supports the DOM, just to take one small example, must return all the P elements in an HTML web page as an array of nodes when the getElementsByTagName method is called against that web page in a script: paragraphs = document.getElementsByTagName(P); // paragraphs[0] is the first p element // paragraphs[1] is the second p element, etc. alert(paragraphs[0].nodeName); All of the properties, methods, and events available to the web developer for manipulating and creating web pages are organized into objects (e.g., the document object that represents the document itself, the table object that implements that special HTMLTableElement DOM interface for accessing HTML tables, and so forth). This documentation provides an object-by-object reference to those APIs. DOM vs. JavaScript The short example above, like all of the examples in this reference, is JavaScript. That is to say, its written in JavaScript, but it uses the DOM to access the web page and its elements. The DOM is not a programming language, but without it, the JavaScript language wouldnt have any model or notion of the web pages, XML pages, and elements with which it is usually concerned. Every element in a document-the document as a whole, the head, tables within the documen