Learning JavaScript, 2nd Edition

Chapter 1. Hello JavaScript!

One reason JavaScript is so popular is that it’s relatively easy to add JavaScript to a web page. All you need to do, at a minimum, is include an HTML script element in the page, specify "text/javascript" for the type attribute, and add whatever JavaScript you want:

<script type="text/javascript">
...some JavaScript
</script>

Installation is not required, nor do you have to torturously work through any odd library path configurations. JavaScript works, straight out of the box and in most web browsers, including the big four: Firefox, Internet Explorer, Opera, and Safari. All you need to do is add a scripting block, and you’re in business.

Traditionally, you add JavaScript blocks to the head element in the document (delimited by opening and closing head tags), but you also can include them in the body element—or even in both sections. However, adding script to the body is not usually considered a good technique, as it makes it more difficult to find the script when you’re modifying it at a later time. The exception to this rule is when performance is an issue, which I’ll cover in Chapter 6. All of the examples in this book add scripting blocks only to the web page head section.

Hello World!

Also traditionally, the first example when learning a new programming language is known as “Hello, World”—a simple application that prints out “Hello, World!” to the user interface, whatever it may be. In the case of JavaScript, the user interface is the web page. Example 1-1 ...