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THE DOCUMENT OBJECT MODEL
When you open a web page, your browser retrieves the page’s HTML text and parses it, much like our parser from Chapter 12 parsed programs. The browser builds up a model of the document’s structure and uses this model to draw the page on the screen.
This representation of the document is one of the toys that a JavaScript program has available in its sandbox. It is a data structure that you can read or modify. It acts as a live data structure: when it’s modified, the page on the screen is updated to reflect the changes.
Document Structure
You can imagine an HTML document as a nested set of boxes. Tags such as <body> and </body> enclose other tags, which in turn contain other tags or text. Here’s the example document ...
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