A Web Document as A Tree of Nodes

JavaScript Tutorials - Herong's Tutorial Examples

∟W3C's Document Object Model (DOM) Specifications

∟A Web Document as A Tree of Nodes

This section provides a tutorial example of JavaScript to show that a Web page is a tree of nodes. This shows the simplified flattened view of DOM API.

We know that a Web page, a HTML document, is a tree of elements (ignoring attributes for a moment). From a simplified point of view, all elements are represented by the "Node" interface. To differentiate different types of nodes from each other, we can check the "type" and "name" attributes.

Now let's walk through the tree and present each element as a node with its type and name with a simple JavaScript example:

<html>
<!-- DOM_API_Simplified_Node_View.html
   Copyright (c) 2013 by Dr. Herong Yang, herongyang.com
-->
<head>
<title>DOM API - Simplified Node View</title>
<style type="text/css">body {background-color: #aaaaff}</style>
<script type="text/javascript">
function showInterface(node, prefix, out) {
   var typeName = new Array("NULL", "ELEMENT", "ATTRIBUTE", "TEXT",
      "CDATA", "ENTITY_REFERENCE", "ENTITY", "RROCESSING_INSTRUCTION",
      "COMMENT", "DOCUMENT", "DOCUMENT_TYPE", "DOCUMENT_FRAGMENT",
      "NOTATION");
   out += prefix+"[Node type="+typeName[node.nodeType]
      +" name="+node.nodeName+"]\n";
   var list = node.childNodes;
   for (var i=0; i<list.length; i++) {
      out = showInterface(list.item(i), prefix+"   ", out);
   }
   return out;
}
function show() {
   var text = document.createTextNode(showInterface(document,"",""));
   var display = document.getElementById("display");
   display.replaceChild(text,display.firstChild);
}
</script>
</head>
<body>
This first text is in the "body" element directly.
<p>This second text is in a "p" element.</p>
<form action="nothing" method="get">
   <input type="button" value="View" onClick="show();"/>
</form>
<pre id="display">
Click the View button to see interface names...
</pre>
</body>
</html>

Notice that I am using an array to translate "node.nodeType" from an integer to a string.

In you run this JavaScript page in Firefox 2.0 and click the "View" button, you will get a nice tree list of nodes with their types and names used in this Web page:

[Node type=DOCUMENT name=#document]
   [Node type=ELEMENT name=HTML]
      [Node type=ELEMENT name=HEAD]
         [Node type=COMMENT name=#comment]
         [Node type=ELEMENT name=TITLE]
            [Node type=TEXT name=#text]
         [Node type=TEXT name=#text]
         [Node type=ELEMENT name=STYLE]
            [Node type=TEXT name=#text]
         [Node type=TEXT name=#text]
         [Node type=ELEMENT name=SCRIPT]
            [Node type=TEXT name=#text]
      [Node type=ELEMENT name=BODY]
         [Node type=TEXT name=#text]
         [Node type=ELEMENT name=P]
            [Node type=TEXT name=#text]
         [Node type=TEXT name=#text]
         [Node type=ELEMENT name=FORM]
            [Node type=TEXT name=#text]
            [Node type=ELEMENT name=INPUT]
            [Node type=TEXT name=#text]
         [Node type=TEXT name=#text]
         [Node type=ELEMENT name=PRE]
            [Node type=TEXT name=#text]
         [Node type=TEXT name=#text]

Table of Contents

About This Book

Introduction to JavaScript

ECMAScript Language Specification and JavaScript Dialects

Data Types, Variables and Expressions

Flow Control Statements

Creating, Accessing, and Manipulating Arrays

Defining and Calling Functions

Web Browser Supporting JavaScript

Server-Side and Client-Side Web Scripting

Introduction to Objects

Defining Your Own Object Types