JavaScript: The Definitive Guide

JavaScript: The Definitive Guide

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by David Flanagan

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This fourth edition of the definitive reference to JavaScript, a scripting language that can be embedded directly in web pages, covers the latest version of the language, JavaScript 1.5, as supported by Netscape 6 and Internet Explorer 6. The book also provides complete coverage of the W3C DOM standard (Level 1 and Level 2), while retaining material on the legacy…  See more details below


This fourth edition of the definitive reference to JavaScript, a scripting language that can be embedded directly in web pages, covers the latest version of the language, JavaScript 1.5, as supported by Netscape 6 and Internet Explorer 6. The book also provides complete coverage of the W3C DOM standard (Level 1 and Level 2), while retaining material on the legacy Level 0 DOM for backward compatibility.

Product Details

O'Reilly Media, Incorporated
Publication date:
Definitive Guides Series
Edition description:
Fourth Edition
Product dimensions:
7.04(w) x 9.14(h) x 1.73(d)

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Chapter 17: The Document Object Model

A document object model (DOM) is an application programming interface (API) for representing a document (such as an HTML document) and accessing and manipulating the various elements (such as HTML tags and strings of text) that make up that document. JavaScript-enabled web browsers have always defined a document object model; a web-browser DOM may specify, for example, that the forms in an HTML document are accessible through the forms[] array of the Document object.

In this chapter, we'll discuss the W3C DOM, a standard document object model defined by the World Wide Web Consortium and implemented (at least partially) by Netscape 6 and Internet Explorer 5 and 6. This DOM standard1 is a full-featured superset of the traditional web-browser DOM. It represents HTML (and XML) documents in a tree structure and defines properties and methods for traversing the tree and examining and modifying its nodes. Other portions of the standard specify techniques for defining event handlers for the nodes of a document, working with the style sheets of a document, and manipulating contiguous ranges of a document.

This chapter begins with an overview of the DOM standard and then describes the core portions of the standard for working with HTML documents. The discussion of the core standard is followed by short sections that explain the DOM-like features of Internet Explorer 4 and Netscape 4. The chapter ends with an overview of two optional parts of the DOM standard that are closely related to the core. Later chapters cover advanced DOM features for working with style sheets and events.

An Overview of the DOM

The DOM API is not particularly complicated, but before we can begin our discussion of programming with the DOM, there are a number of things you should understand about the DOM architecture.

Representing Documents as Trees

HTML documents have a hierarchical structure that is represented in the DOM as a tree structure. The nodes of the tree represent the various types of content in a document. The tree representation of an HTML document primarily contains nodes representing elements or tags such as <body> and <p> and nodes representing strings of text. An HTML document may also contain nodes representing HTML comments.2 Consider the following simple HTML document:

    <title>Sample Document</title>
    <h1>An HTML Document</h2>
    <p>This is a <i>simple</i> document.

The DOM representation of this document is the tree pictured in Figure 17-1.

If you are not already familiar with tree structures in computer programming, it is helpful to know that they borrow terminology from family trees. The node directly above a node is the parent of that node. The nodes one level directly below another node are the children of that node. Nodes at the same level, and with the same parent, are siblings. The set of nodes any number of levels below another node are the descendants of that node. And the parent, grandparent, and all other nodes above a node are the ancestors of that node.


The DOM tree structure illustrated in Figure 17-1 is represented as a tree of various types of Node objects. The Node interface3 defines properties and methods for traversing and manipulating the tree. The childNodes property of a Node object returns a list of children of the node, and the firstChild, lastChild, nextSibling, previousSibling, and parentNode properties provide a way to traverse the tree of nodes. Methods such as appendChild( ), removeChild( ), replaceChild( ), and insertBefore( ) enable you to add and remove nodes from the document tree. We'll see examples of the use of these properties and methods later in this chapter.

Types of nodes

Different types of nodes in the document tree are represented by specific subinterfaces of Node. Every Node object has a nodeType property that specifies what kind of node it is. If the nodeType property of a node equals the constant Node.ELEMENT_NODE, for example, you know the Node object is also an Element object and you can use all the methods and properties defined by the Element interface with it. Table 17-1 lists the node types commonly encountered in HTML documents and the nodeType value for each one.

Table 17-1: Common node types


nodeType constant

nodeType value



















The Node at the root of the DOM tree is a Document object. The documentElement property of this object refers to an Element object that represents the root element of the document. For HTML documents, this is the <html> tag that is either explicit or implicit in the document. (The Document node may have other children, such as Comment nodes, in addition to the root element.) The bulk of a DOM tree consists of Element objects, which represent tags such as <html> and <i>, and Text objects, which represent strings of text. If the document parser preserves comments, those comments are represented in the DOM tree by Comment objects. Figure 17-2 shows a partial class hierarchy for these and other core DOM interfaces.


The attributes of an element (such as the src and width attributes of an <img> tag) may be queried, set, and deleted using the getAttribute( ), setAttribute( ), and removeAttribute( ) methods of the Element interface.

Another, more awkward way to work with attributes is with the getAttributeNode( ) method, which returns an Attr object representing an attribute and its value. (One reason to use this more awkward technique is that the Attr interface defines a specified property that allows you to determine whether the attribute is literally specified in the document, or whether its value is a default value.) The Attr interface appears in Figure 17-2, and it is a type of node. Note, however, that Attr objects do not appear in the childNodes[] array of an element and are not directly part of the document tree in the way that Element and Text nodes are. The DOM specification allows Attr nodes to be accessed through the attributes[] array of the Node interface, but Microsoft's Internet Explorer defines a different and incompatible attributes[] array that makes it impossible to use this feature portably....

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Javascript 4.2 out of 5 based on 0 ratings. 14 reviews.
Computer_Science_House More than 1 year ago
JavaScript: The Definitive Guide by David Flanagan is probably the best reference possible for this extremely useful, but complex language. I came to this book with absolutely no knowledge of Javascript, and so this book was my first real taste of the language. The first part of the book deals specifically with syntax and foundations of Javascript, so anyone with programming experience can read the first part of this book and be comfortable with programming in Javascript. This section is integral for understanding the nuanced complexities of a language without having to struggle with hard to find errors. Simple distinctions of types and values were very helpful to me.

The second part of the book is a by-examples tour through the intermingled worlds of Javascript and web browsers. Here you¿ll learn DOM scripting, AJAX, DHTML events, and more to make appealing interactive webpages. Personally, I found this section a little harder to use, and I would have preferred a, perhaps simpler, or at least more atomic explanation of AJAX as I am still confused by the whole concept. In either case, this section covers everything you need to know about Web 2.0.

The last two sections of the book are straight reference about everything in the core of Javascript and in client-side Javascript. This is a very well organized section of the book and it helps when you need to know exactly how a certain method or class works and this section alone is worth the cost of the book.

I'd recommend this book to anyone who wants to get a taste of Javascript or for anyone who is looking towards Javascript as a way to access web programming. The book is not for everyone, but I would argue that Javascript is a very important language to learn in this web-centric age.
Guest More than 1 year ago
You can't get a better book on Javascript than this!
Guest More than 1 year ago
If you purchase only one JavaScript book let it be this one. The content is thorough and insightful. The writing style won't put you to sleep! After you have core JavaScript principles down you will keep this book nearby for reference. This book will give you the foundation and drive to move forward. Whether you are writing JavaScript for web pages, JavaScript for PhotoShop, or writing in SwishScript for SwishMax, you can use this book to chart your course. It's well worth the money.
Guest More than 1 year ago
'JavaScript: The Definitive Guide' is not a step by step guide to JavaScript any more than an encyclopedia is a step by step guide. The book does provide an authoritative analysis of the language including a brief history of the language, data types, operators, statements, functions, objects, and arrays. The author does a good job of addressing some of the assumptions of the language and how these assumptions may or may not be like other languages such as C++ or Java. The author also clarifies the different levels of support for certain aspects of the language both within the discussion and with the large JavaScript reference section. The book also provides a handy and thorough W3C DOM reference for working with various aspects of DHTML. Some of the material in this book will provide a critical understanding to JavaScript's more advanced features. With the emergence of AJAX, many web developers are turning to JavaScript to provide solutions for dynamic web based applications. Now that JavaScript is more fully supported in modern browsers, web developers may want to turn to 'JavaScript: The Definitive Guide' to enhance or polish existing JavaScript skills. If you are looking for a quick introduction to JavaScript, you may find yourself disappointed. However, if you are already familiar with JavaScript and need a reference to look up an answer to your problem or need a guide for fine tuning your DHTML skills, you may that this book is a rich resource for you.
Guest More than 1 year ago
I am an applications programmer who has had to turn into a web programmer for a special project in my field. Before reading this book, I knew some HTML from my college days, but was overwhelmed by the project before me. I bought this book at a B&N store after debating between at least three other competitors. I am SO glad I bought this one! It has helped me get my project off the ground! I now feel comfortable with JavaScript and should be able to handle other web projects that come my way.
Guest More than 1 year ago
This book is the best JavaScript resource around, but a word of warning to those who expect it to be like the Visual QuickStart series: It's not. This is a programmer's book about a real programming language, it's not a cut and paste example guide. They both have their place in the world, but this book should not be downgraded because it is the former and not the latter. If you're serious about learning JS as a programming language, and have taken at least one solid course in programming concepts, this is the place to go.

The previous reviewer summed it up well. Due to wildly diverging implementations, this book doesn't necessarily cover everything, but it's about as close as one can get and remain sane. For the rest, pick up the O'Reilly Dynamic HTML, or just consult on-line documentation.

Until I started programming server-side Java, this book was, by far, the most used book on my desk.

Guest More than 1 year ago
When I picked up this book in 1998, I knew absolutely no JavaScript. I sat down to read the first chapter, and stopped after the 10th or so, finally realizing that everyone else had long since gone to sleep. This book has held my attention ever since. I was going to give it 4 stars because it is somewhat dated and lacks modern DOM documentation, but I just couldn't. That would be punishing for being so good -- so good that it hasn't needed updating, that is. Besides, this isn't a DOM book. Pair it with Danny Goodman's book on Dynamic HTML, and you'll have everything you need for almost every client-side task. My one criticism: I found myself wanting more discussion of Regular Expressions.
Guest More than 1 year ago
This is an excellent reference source for the javascript programmer.
Guest More than 1 year ago
Despite the reviews written here, I think this book is spiffing. Granted, it's not for complete beginners, but then again - its a programming language - so what do you expect??!! Its ideal for someone who has good programming skills and wants to learn JavaScript as a string to their bow.
Guest More than 1 year ago
Good: generally thorough, well-written. Bad: no CD-ROM (examples would have been great), differences between IE and Navigator not thoroughly treated.
Guest More than 1 year ago
I wanted to enhance my web design skills by learning JavaScript. This is not the book to purchase if you are a non-programmer. I found it very hard to understand and did not get a thing out of any of their examples.
Guest More than 1 year ago
Do not buy this book if you are not already a programmer - as it will only discourage you. This book throws around programming terms and constant C and C++ references, as if the author wanted to show you that he is a 'real' programmer, and that this javascript thing is just a hobby for him. I don't have a grudge against O'Reilly - I realize that many people consider this to be the de facto standard javascript book - but if you are a web-designer that comes from a non-programming background as I do, this book will be useless to you.
Guest More than 1 year ago
This is a nice book if you already know C or C++ and are trying to learn JavaScript. The author frequently points out the similarities and differences between JavaScript and other languages. I found this helpful because I wasn't bored with things I already knew. The reference section takes up half of the book and seems well-organized and comprehensive. However, if you know nothing about programming, you will probably find this book boring or a little over your head. Don't waste your time on it unless you already know a language.
Guest More than 1 year ago
Offers a good starting place for beginner programmers and an excellent reference section for experienced programmers.