AJAX and Flash have matured into powerful, stable software platforms that can support nearly any sort of application. The question “which technology do I need to use?” has become “which technology am I most comfortable with?” The final decision may have more to do with the process and tools you are familiar with and the resources that are available to you than the limitations of a particular technology.

That said, there are areas where one or the other clearly wins out. As we have seen with the rise of YouTube and its countless imitators, video is an area where Flash has become dominant. Conversely, template-driven sites with significant back-end integration are still almost always built with HTML, CSS and JavaScript. As a developer, it is your job to understand the pros and cons of each, and to make intelligent choices.

Before pitting them head to head, we want to provide a brief overview of each technology.

Adam Pasztory, a web developer with a host of experience in web development and consultation, outlines the merit in making comparisons between Flash and AJAX. The feature continues with a case for each technology and concludes with an overview on the epic duel.

No technology provides a perfect solution to the problems you will face as a developer. You want to select the best tools for the job at hand. As a developer, it is important to be familiar with a variety of technologies and to be able to compare their strengths and weaknesses. When a client comes to me with a new project, I try to give them a fair opinion about what the best approach will be for them. The last thing you want to do is to force them to use a technology that they are not happy with. A lot of companies simply don’t have a high comfort level with Flash, so you may need to sell them on it by explaining the potential benefits. AJAX is usually an easier sell to clients because it is more closely related to familiar technologies.

AT THE TIME when AJAX arrived on the scene, Flash was going through significant growing pains. Adobe acquired Macromedia, and many Flash developers feared that the unique vision that made Flash special would be lost. Indeed, the most exciting advances in Flash were coming from the open source community. Meanwhile, Microsoft was waiting in the wings with its new RIA technology, Silverlight.

Fortunately, the Adobe management were smart enough keep their hands off and let the former Macromedia employees keep doing what they did best. The company quickly put any scepticism about the merger to rest by unleashing a slew of new technologies related to Flash that were greeted positively by the developer community. It didn’t hurt that these new technologies underwent extensive public beta periods on the Adobe Labs site, during which developers could acquaint themselves with the tools for free.

The Flash Player 9 upgrade introduced mind-blowing performance improvements that made learning the new language worthwhile. Real-time 3D graphics and online video suddenly became a reality. And in a bit of a departure from previous release cycles, major new features, such as fullscreen mode, were released as minor upgrades to Flash 9 as they became available. With ActionScript 3, they rewrote the underlying of Flash from the ground up. AS2, while useable, was a hotchpotch of inconsistent usage due to its dependency on previous versions of the Flash Player. By drawing a line of demarcation with AS3 and essentially rewriting all their objects from scratch, Adobe engineers made a bold break from the past.

Finally, with Flex Builder, Adobe created a development environment targeted squarely at developers as opposed to artists and designers. Professional programmers often dismissed the Flash Authoring Environment (or IDE) as simply an art program because it didn’t look like a typical programming environment. Flex Builder allows developers to write their Flash programs in an IDE called Eclipse, which is popular among Java developers. To get started in Flash, it was no longer necessary for programmers to learn arcane concepts like timelines and Movie Clips. Moreover, Flex Builder shipped with a slick set of user interface components that were easy to get running in minutes. Previous attempts to introduce standard components into Flash had been a debacle, so the Flex components represented a major breakthrough.

AJAX IS NOT so much a particular technology, but a movement. The individual components of AJAX existed as far back as the mid-Nineties, but the movement did not coalesce until Google and a few other prominent companies championed AJAX with killer apps that ushered in the age of Web 2.0. AJAX became a more practical option as PCs became faster. JavaScript running in a browser is particularly slow because unlike ActionScript, it is interpreted by the browser at runtime. An analogy would be a multilingual speaker attempting to perform a live translation of a written work, as opposed to translating it ahead of time. AJAX gained traction because it no longer mattered that JavaScript running in a browser was slow – it was fast enough.

When AJAX first came on the scene, proponents argued it was inherently superior to Flash because it was based on the core technology of the web. To them, AJAX promised to eliminate the confusing interfaces and other usability problems that seemed to appear in every Flash application. This was a mistaken assumption. What people didn’t acknowledge was that the ascension of AJAX was part of an evolution from web pages to web applications. Links and simple controls were no longer adequate to express the functionality needed to take the web to the next level (Web 2.0). A slew of widgets were written including tabs, menus, slider bars, colour pickers and interactive charts. Though some of these widgets were fantastic, many were no less confusing than Flash UIs, and they were hampered by performance issues.

AJAX developers also had to adapt themselves to the methodology of building state-based applications. That is, when a user takes some action on a page, the browser does not load a new page but rather reconfigures the current page to a new state. Integrating state-based applications into a web browser presents significant design challenges: what happens if the user pushes the Back button? Does the application undo the last action on the page or does it load the previous page? What happens if the user tries to bookmark the page in its current state? Can the application return to the bookmarked state or is work lost? Flash developers had already been struggling with these problems for years.

Cross-browser compatibility issues have also been a scourge on even the most erstwhile AJAX developer. It horrifies us to contemplate the countless hours the developer community must have lost to minor browser glitches. How simple life would be with Firefox, Opera and Safari, but no IE.

AJAX might have died a premature death had not a slew of libraries and frameworks swooped in to save the day. It seemed a new AJAX framework would pop up nearly every day, but now a few have risen to the top: notably Dojo, jQuery and Prototype on the open source side, ASP.net AJAX from Microsoft, Google Web Toolkit (GWT), Spry from Adobe and the Yahoo! UI Library. Frameworks vary greatly in approach. For example, GWT is written using Java and then compiled down to JavaScript. However, frameworks share the goal of making programming more pleasurable by enforcing consistency, and allowing the developer to write code that can run in any browser.

This brings us to the Flash platform, which shares the same goals with AJAX frameworks but tries to remove the browser from the equation entirely by isolating the application within the Flash Player.

The chart that accompanies this article identifies key components of a web application and attempts to declare a winner for each one. In some cases, it was a very close call. Of course, developers have to make choices based on the nature of the application they must build. As a general rule, applications that are comprised primarily of text and static images are best created in AJAX. On the other hand, multimedia applications and games more naturally align with Flash’s feature set.

My hope for the future is a world where Flash and AJAX can coexist seamlessly. Perhaps the future is not so far off. Already, with a language called Haxe (www.haxe.org) you can compile the same program into Flash (both 8 and 9) and JavaScript. Meanwhile, Mozilla and Adobe are working on the Tamarin Project (www.mozilla.org/ projects/tamarin), which aims to unite ActionScript and JavaScript as a single language. Until this perfect future, we must do the best with the tools we have. Fortunately, they are an impressive set of tools, and the future is bright regardless of which side your loyalties lie.