Datasheet

In this book we only scratch the surface of XPath’s capabilities, but if you want to learn how to build

more complex XPath expressions, you can read more about the language and its capabilities on the W3C

web site.

JavaScript and DOM

JavaScript is another scripting language, widely known for its use in web-based applications. The

name JavaScript is something of a misnomer, as it bears only a superficial resemblance to the Java pro-

gramming language. It first appeared in Netscape’s web browser in 1995, and was incorporated into the

international standard ECMA-262 as ECMAScript. Most modern browsers incorporate an ECMAScript-

compatible scripting language — the one found in Microsoft’s Internet Explorer is known as Jscript.

JavaScript is actually a registered trademark of Sun Microsystems, but is widely used as a generic refer-

ence to the scripting language used within web browsers.

Within the scripting language, web browsers typically implement the W3C standard DOM, or

document

object model

. The DOM specifies how HTML and XML documents are represented as a tree structure

within the browser. The DOM specification also specifies the programmatic interface by which the vari-

ous elements within the document tree can be manipulated.

JavaScript used to manipulate the DOM within a browser is often referred to as

dynamic HTML. Here’s a

simple example of how you might use dynamic HTML to provide interaction on a web page.

<html>

<head>

<title>Arithmetic</title>

function showAnswer()

{

var answerNode = document.getElementById(‘answer’);

answerNode.innerHTML = “<h2>Answer</h2><p>” + (2 + 2) + “</p>”;

}

</script>

</head>

<body>

<h1>Question</h1>

<p>

What is the answer to the sum <code>2 + 2</code>?

</p>

</form>

The answer will appear here

</div>

</body>

</html>

In this example, the question is placed inside a form, with a button to submit the form and show the

answer. A placeholder

<div> element is added at the end of the document and is where the answer to

the question will appear.

Chapter 1: Rewriting the Web

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