Understanding the DOM_Learning jQuery（Fourth Edition）-QQ阅读男频历史网

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Understanding the DOM

One of the most powerful aspects of jQuery is its ability to make selecting elements in the DOM easy. The DOM serves as the interface between JavaScript and a web page; it provides a representation of the source HTML as a network of objects rather than as plain text.

This network takes the form of a family tree of elements on the page. When we refer to the relationships that elements have with one another, we use the same terminology that we use when referring to family relationships: parents, children, and so on. A simple example can help us understand how the family tree metaphor applies to a document:

<html>
  <head>
    <title>the title</title>
  </head>
  <body>
    <div>
      <p>This is a paragraph.</p>
      <p>This is another paragraph.</p>
      <p>This is yet another paragraph.</p>
    </div>
  </body>
</html>

Here, <html> is the ancestor of all the other elements; in other words, all the other elements are descendants of <html>. The <head> and <body> elements are not only descendants, but children of <html> as well. Likewise, in addition to being the ancestor of <head> and <body>, <html> is also their parent. The <p> elements are children (and descendants) of <div>, descendants of <body> and <html>, and siblings of each other.

To help visualize the family tree structure of the DOM, we can use a number of software tools, such as the Firebug plugin for Firefox or the Web Inspector in Safari or Chrome.

With this tree of elements at our disposal, we'll be able to use jQuery to efficiently locate any set of elements on the page. Our tools to achieve this are jQuery selectors and traversal methods.