Ajax Interview Questions and Answers
Ques 1. What's AJAX ?
AJAX (Asynchronous JavaScript and XML) is a newly coined term for two powerful browser features that have been around for years, but were overlooked by many web developers until recently when applications such as Gmail, Google Suggest, and Google Maps hit the streets.
Asynchronous JavaScript and XML, or Ajax (pronounced "Aye-Jacks"), is a web development technique for creating interactive web applications using a combination of XHTML (or HTML) and CSS for marking up and styling information. (XML is commonly used, although any format will work, including preformatted HTML, plain text, JSON and even EBML).
The Document Object Model(DOM) manipulated through JavaScript to dynamically display and interact with the information presented.
The XMLHttpRequest object to exchange data asynchronously with the web server. In some Ajax frameworks and in some situations, an IFrame object is used instead of the XMLHttpRequest object to exchange data with the web server.
Like DHTML, LAMP, or SPA, Ajax is not a technology in itself, but a term that refers to the use of a group of technologies together. In fact, derivative/composite technologies based substantially upon Ajax, such as AFLAX, are already appearing.
Ajax applications are mostly executed on the user's computer; they can perform a number of tasks without their performance being limited by the network. This permits the development of interactive applications, in particular reactive and rich graphic user interfaces.
Ajax applications target a well-documented platform, implemented by all major browsers on most existing platforms. While it is uncertain that this compatibility will resist the advent of the next generations of browsers (in particular, Firefox), at the moment, Ajax applications are effectively cross-platform.
While the Ajax platform is more restricted than the Java platform, current Ajax applications effectively fill part of the one-time niche of Java applets: extending the browser with portable, lightweight mini-applications.
Ques 2. Who's Using Ajax ?
Google is making a huge investment in developing the Ajax approach. All of the major products Google has introduced over the last year? Orkut, Gmail, the latest beta version of Google Groups, Google Suggest, and Google Maps are Ajax applications. (For more on the technical nuts and bolts of these Ajax implementations, check out these excellent analyses of Gmail, Google Suggest, and Google Maps.) Others are following suit: many of the features that people love in Flickr depend on Ajax, and Amazon's A9.com search engine applies similar techniques.
These projects demonstrate that Ajax is not only technically sound, but also practical for real-world applications. This isn't another technology that only works in a laboratory. And Ajax applications can be any size, from the very simple, single-function Google Suggest to the very complex and sophisticated Google Maps.
Ques 3. Should I consider AJAX?
AJAX definitely has the buzz right now, but it might not be the right thing for you. AJAX is limited to the latest browsers, exposes browser compatibility issues, and requires new skill-sets for many. There is a good blog entry by Alex Bosworth on AJAX Mistakes which is a good read before you jump full force into AJAX.
On the other hand you can achieve highly interactive rich web applications that are responsive and appear really fast. While it is debatable as to whether an AJAX based application is really faster, the user feels a sense of immediacy because they are given active feedback while data is exchanged in the background. If you are an early adopter and can handle the browser compatibility issues, and are willing to learn some more skills, then AJAX is for you. It may be prudent to start off AJAX-ifying a small portion or component of your application first. We all love technology, but just remember the purpose of AJAX is to enhance your user's experience and not hinder it.
Ques 4. Does AJAX work with Java?
Absolutely. Java is a great fit for AJAX! You can use Java Enterprise Edition servers to generate AJAX client pages and to serve incoming AJAX requests, manage server side state for AJAX clients, and connect AJAX clients to your enterprise resources. The JavaServer Faces component model is a great fit for defining and using AJAX components.
Ques 5. Won't my server-side framework provide me with AJAX?
You may be benefiting from AJAX already. Many existing Java based frameworks already have some level of AJAX interactions and new frameworks and component libraries are being developed to provide better AJAX support. I won't list all the Java frameworks that use AJAX here, out of fear of missing someone, but you can find a good list at www.ajaxpatterns.org/Java_Ajax_Frameworks.
If you have not chosen a framework yet it is recommended you consider using JavaServer Faces or a JavaServer Faces based framework. JavaServer Faces components can be created and used to abstract many of the details of generating JavaScript, AJAX interactions, and DHTML processing and thus enable simple AJAX used by JSF application developer and as plug-ins in JSF compatible IDE's, such as Sun Java Studio Creator.
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