JavaScript Support in Web Browsers

This section provides a quick description of how Web browsers execute JavaScript codes, provide DOM API for document interaction, and provide events to trigger JavaScript code execution.

A typical Web browser will provide support to JavaScript in 4 areas:

Let's use a simple JavsScript example to illustrate those areas:

<html>
<!-- DOM_and_Event.html
   Copyright (c) 2013 by Dr. Herong Yang, herongyang.com
-->
<head>
<title>DOM and Event</title>
<script type="text/javascript">
var colorID = 0;
function changeColor() {
   if (colorID == 0 )
      document.body.bgColor = "lightgrey";
   else if (colorID == 1 )
      document.body.bgColor = "lightblue";
   else if (colorID == 2 )
      document.body.bgColor = "lightgreen";
   else if (colorID == 3 )
      document.body.bgColor = "lightyellow";
   colorID = (colorID+1)%4;
}
</script>
</head>
<body>
<p>
<script type="text/javascript">
   document.write('Hello World!');
</script>
</p>
<form>
  <input type="button" value="Click to change background color"
   onClick="changeColor();"/>
</form>
<p>Want to know the color code? 
<a href="javascript:alert(document.body.bgColor)">Click here.</a>
</p>
</body>
</html>

Run this JavaScript example in a Web browser, and click the change color button. The browser will change the background color of the page each time you click the button.

If you want to know the code value of the current background color, you can click the hyper link near the end of the page.

Now look at the JavaScript example again. The browser indeed supports you in 4 areas:

1. Executes the JavaScript code included in the "script" tag while rendering the HTML document:

<script type="text/javascript">
   document.write('Hello World!');
</script>

2. Provides the "document" object as part of the DOM API to allow the JavaScript code to interact with the HTML document:

   document.write('Hello World!');
   document.body.bgColor = "lightgrey";
   ...

3. Provides the "onClick" event to allow the JavaScript code to be executed:

  <input type="button" value="Click to change background color"
   onClick="changeColor();"/>

4. Executes the JavaScript code included in "javascript:" pseudo-URL.

<a href="javascript:alert(document.body.bgColor)">Click here.</a>

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

JavaScript Support in Web Browsers

 Including JavaScript Codes with HTML "script" Tags

 Including 'script' Tags in String Literials

 Escaping 'script' Tags in String Literials

 Using HTML Entities to Protect HTML Tags

 Including JavaScript Codes as External Files

 DOM API - The "document" Object

 DOM API - The "window" Object

 DOM API - The "window.open" Method

 Event Listeners and Objects

 'javascript:' Pseudo-URL Addresses

 Server-Side and Client-Side Web Scripting

 Introduction to Objects

 Defining Your Own Object Types

 Inheritance of Properties and Methods through the Prototype Object Chain

 'jrunscript' - JavaScript Shell Command from JDK

 Using Functions as "Function" Objects

 Introduction to Built-in Object Types

 W3C's Document Object Model (DOM) Specifications

 References

 PDF Printing Version