Advantages and Disadvantages of AJAX

Now Mr. Pravin presents reasons to use and why not to use 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. 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.

3. 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.

4. 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.

5. Real-Time Form Data Validation: Form data such as user IDs, serial numbers, postal codes, or even special coupon codes that require server-side validation can be validated in a form before the user submits a form.

6. Auto completion: A specific portion of form data such as an email address, name, or city name may be auto completed as the user types.

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.

3. 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.

4. 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. "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.

5. 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.
Furthermore, 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.

6. Debugging: AJAX applications are also difficult to debug because the processing logic is embedded both in the client and on the server.

7. Viewable Source: The client-side JavaScript technology may be viewed simply by selecting View Source from an AJAX-enabled HTML page. A poorly designed AJAX-based application could open itself up to hackers or plagiarism (illegal use or stealing or copying).

8. 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.
Given these advantages and disadvantages of AJAX, you have to decide whether you need to use it or not before you start the design and implementation of your next project
The AJAX approach to building web applications shed a new light on the web and help close the gap between web applications and desktop applications in terms of usability and responsiveness. As the technique approaches maturity, many benefits and pitfalls will be uncovered, but the overall principles promise to revolutionize the web as we know it.