↑
Main Page

noscript tag

on the following line. Next, you see the function definition as usual. The second-to-last line is the most

interesting because it starts with a JavaScript single-line comment (the two forward slashes) and then

continues with the close of the HTML comment (

-->

). This line is still considered part of the JavaScript

code, so the single-line comment notation is necessary to avoid a syntax error. However, older browsers

only acknowledge the close of the HTML comment and, therefore, ignore all the JavaScript code. A

browser that supports JavaScript, however, just ignores this line and continues on to the closing

</script>

tag.

Although this method of code-hiding was very prevalent in the early days of the Web, it is not as neces-

sary today. Presently, most of the popular Web browsers support JavaScript, and those that don’t often

are smart enough to ignore the code on their own. It is completely up to you whether you choose to use

this method, but keep in mind that using external JavaScript files inside of inline code is a much easier

method of hiding code from older browsers.

The <noscript/> tag

Another concern over browsers without JavaScript is how to provide alternate content. Hiding the code

was part of the solution, but developers wanted a way to specify content that should appear only if

JavaScript wasn’t available. The solution came in the form of the

tag, that can contain any

HTML code (aside from

). This HTML code is ignored by browsers that support JavaScript

and have it enabled; any browser that doesn’t support JavaScript or has it disabled renders the content

. For example:

<html>

<head>

<title>Title of Page</title>

function sayHi() {

alert(“Hi”);

}

</script>

</head>

<body>

sayHi();

</script>

<p>Your browser doesn’t support JavaScript. If it did support

JavaScript, you would see this message: Hi!</p>

</noscript>

<p>This is the first text the user will see if JavaScript is enabled. If

JavaScript is disabled this is the second text the user will see.</p>

</body>

</html>

In this example, the

tag is included with a message telling the user that the browser

doesn’t support JavaScript. Chapter 8, “Browser and Operating System Detection,” explains a practical

way of using

130

Chapter 5

08_579088 ch05.qxd 3/28/05 11:37 AM Page 130