Working with JavaScript in Drupal 6: Part 1

How Drupal handles JavaScript
How is JavaScript typically used? Mostly, it is used to provide additional functionality to a web page, which is usually delivered to a web browser as an HTML document. The browser receives the HTML from the server and then begins the process of displaying the page. During this parsing and rendering process, the browser may request additional resources from the server such as images, CSS, or Flash. It then incorporates these elements into the document displayed to the user.

In this process, there are two ways that JavaScript code can be sent from the server to the browser. First, the code can be placed directly inside the HTML. This is done by inserting code inside the <script> and </script> tags:

<script type="text/javascript">
alert('hello world');
</script>

This is called including the script inline.

Second, the code can be loaded separately from the rest of the HTML. Again, this is usually done using the <script> and </script> tags. However, instead of putting the code between the tags, we use the src attribute to instruct the browser to retrieve an additional document from the server.

<script type="text/javascript" src="some/script.js"></script>

In this example, src="some/script.js" points the browser to an additional script file stored on the same server as the HTML document in which this script tag is embedded. So, if the HTML is located at http://example.com/index.html, the browser will request the script file using the URL http://example.com/some/script.js.

The </script> tag is required

When XML was first standardized, it introduced a shorthand notation for writing tags that have no content. Instead of writing <p></p>, one could simply write <p/>. While this notation is supported by all modern mainstream browsers, it cannot be used for <script></script> tags. Some browsers do not recognize <script/> and expect that any <script> tag will be accompanied by a closing </script> tag even if there is no content between the tags.

If we were developing static HTML files, we would simply write HTML pages that include <script></script> tags anytime we needed to add some JavaScript to the page. But we're using Drupal, not static HTML, and the process for adding JavaScript in this environment is done differently. [..]

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