The standards for an impressive Internet presentation have changed substantially since Tim Berners-Lee created the first web pages. Internet sites increasingly remind the surfer of interactive desktop applications rather than printed material. AJAX is a technology based on JavaScript that adds convenience, with pull-down menus, sortable tables, and interactive input pages. The main improvement is the absence of delays typically experienced while pages reloaded.

Long Way

Before rendering a website, the browser and web server go through a number of steps (Figure 1):

• The browser sends a page request to a web server.
• The server processes the request and serves up the HTML text and images. This might take a couple of seconds if the load is heavy. The network transmission speed decides how fast the content is delivered. The required time is still noticeable on fast intranets, however.
• Finally, the browser reads the response and displays the page. The same sequence is repeated for each image before the browser can render the final version of the page.

All told, these three steps typically take several seconds. In case of HTML pages without AJAX technology the steps are repeated for even the tiniest of changes.

In contrast to rich client applications, this considerably affects the user experience: Menus that drop down without a delay, point and click sorting in tables, or drag and drop are not easily implemented because of time-consuming page reloads. HTML pages that offer these kinds of features need to be autonomous, like local programs; that is, you should not need to rely on a server connection.

Figure 1: Pingpong: The exchange between browser and web server that occurs for each page change without AJAX typically takes several seconds.

Removing Time-Consuming Requests

To improve the user experience, more and more web applications are starting to process user input directly browser-side and to do without time-consuming server requests.

Only two of the various techniques for browser-side data processing have achieved widespread success: JavaScript and Flash. Both are available on more than 90 percent of all computers. This means that web developers need not have any qualms about using them.

Other solutions, with the exception of the relatively widespread Java plugin, have been unable to achieve similar multi-platform success. Flash and JavaScript adopt completely different approaches.

Flash

The proprietary Flash plugin executes binary Flash applications in the browser. The plugin is embedded in the web page very much like a bitmap image, except that it offers the user an interactive interface. The Flash plugin has excellent graphics capabilities with virtually no restrictions on the developers' creativity. However, for lack of equivalent open source alternatives, there is virtually no alternative to the Adobe tools.