Ajax advantage and Disadvantage

Why use AJAX?

Building a web application that employs AJAX is more difficult than building it the classic way. You need to go to extra lengths to make sure that the user experience is and remains enjoyable, and not plain annoying. With all the hype going around AJAX, a lot of applications that do not have a real need for it have been built. These are toys meant to prove that AJAX is fun, but with little or no use in real-life situations. At the same time, some applications that do not use AJAX are labeled as such. You can find a list of AJAX applications by using a search engine, or directly here.

The decision whether an application would benefit from using AJAX or not is entirely up to the developer. Here are a few hints to help you take the right decision.

The Benefits of AJAX

To help you decide whether AJAX is for you or not, here are some of the advantages it has over classic web development techniques:

1. The interface is much more responsive, as explained before, because only a small part of the page is transferred at a time. The user has the feeling that changes are instantaneous.
2. In a classic web application, when the web server sends a web page to the browser, it can use multiple connection threads to speed up delivery. However, this happens for content only – what is between the tags. All script and CSS files linked in the page's section are transferred using only one connection thread, which diminishes performance. With AJAX, you only have to load the basic scripts and CSS files, and request the rest as content, through multiple connections.
3. Waiting time is reduced – when the visitor submits a form, they no longer have to wait for the entire page to be rebuilt and re-transmitted by the server. Instead, only the relevant content changes, and in non-critical cases, the visitor can still work while the data is being submitted.
4. If a page section encounters an error, other sections are not affected (if not logically linked) and the data already entered by the user is not lost. This way, the application fails graciously, without causing head-aches for the users.
5. Traffic to and from the server is reduced considerably – because you do not have to send the entire page content (CSS, images, static sections), the bandwidth usage is most likely to decrease.

The Disadvantages of AJAX

As with most new web development techniques, AJAX has its critics. There are a couple of disadvantages that need to be considered before considering an AJAX-based solution:

1. Building an AJAX-powered application can increase development time and costs. It is usually considered more difficult than building a classic web application, because of the mixture of technologies and the special concern about everything going smoothly. However, because it is dealing with relatively known technologies, AJAX is not rocket science.
2. Although AJAX relies on existing and mature technologies like Javascript, HTML and CSS, the available frameworks and components still need to completely mature. Tools like the Dojo toolkit or the Rico framework are just a milestone on this long road. More frameworks that target a specific area are likely to come your way. At InterAKT Online, we're also working on an AJAX-based e-commerce platform to be announced soon. We also released a free JavaScript editor for the Eclipse platform, that you can download from our site.
3. Not all concerns regarding security and user privacy have been answered. This fueled a wave of criticism about how safe is the AJAX way of building applications. Earle Castledine points out some of his concerns regarding user privacy in this article from DevX.com.
4. Using AJAX to asynchronously load bits of content into an existing page conflicts with the way we are used to navigate and create bookmarks in modern browsers. Because viewing some part of the page information no longer corresponds to a newly loaded page, the browser history and bookmarks will not be able to restore the exact page state. Also, clicking the Back button in a browser might not have any effect, since the URL was unchanged (even if parts of the page were changed). To overcome these problems you must implement a way to save the current page state so that it can be restored later on, when called from a bookmark or from the browser history.
5. AJAX is not meant to be used in every application. One of the main reasons for this stays in the fact that Google cannot index it. Consider this basic example that Alexandru Costin, the co-founder of InterAKT Online, pointed out: "Suppose you are building an e-commerce site. A complete AJAX application would be a mistake because search engines won't be able to index it. And without a search engine, a site won't be able to sell products." Keeping this in mind, a much better idea than creating complete AJAX applications would be to scatter AJAX features within the application.
6. The biggest concern with AJAX is accessibility. This is because not all browsers (especially older ones) have complete support for JavaScript or the XMLHttpRequest object. Some of the visitors do have browsers with the required features, but they choose or have to turn off JavaScript support. When you design the application you must make sure that a fail-safe solution exists for those users, so it can be accessed by anyone. Further more, the way to access and use the XMLHttpRequest object in Internet Explorer and other browsers is different, which leads to a fork in the code and the need to treat each case separately.
7. The last disadvantage lies in the actual XMLHttpRequest object itself. Due to security constraints, you can only use it to access information from the host that served the initial page. If you need to display information from another server, it is not possible within the AJAX paradigm.