Top 15 AJAX Interview Questions ? and How to Answer Them

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AJAX (Asynchronous JavaScript and XML) is extremely popular within the web application community for a number of reasons:

AJAX allows the asynchronous updating of web pages through the exchange of data with web servers in real time behind the scenes. This can be done without the need to reload the entire web page.
AJAX is not specifically a language per se but is a technology that facilitates communication from a client-side web page to a database server, updating the web page without reloading the entire page.
The result is a methodology that allows developers to create interactive web applications better and faster.
AJAX combines the best of Cascading Style Sheets (CSS) for presentation, XHTML for managing content, and JavaScript with the Document Object Model (DOM) for display of content.

With all these attributes of an AJAX development platform, application developers are in high demand for building high-performance, functional web pages.

Once you have honed your AJAX development skills, gaining employment as a developer means making a positive impression in a job interview (or two) based on your comprehension of AJAX techniques and your technical knowledge of the functionality.

Anticipating the top AJAX interview questions and knowing how to answer them promptly, specifically, and confidently will go a long way toward acing that interview.

Basic Interview Questions

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When you interview for an AJAX developer position, there are going to be some basic questions that any prospective employer will ask:

How long have you been using JavaScript and AJAX?
How did you learn and become proficient with AJAX ? classroom course, books, video tutorials, a combination, or employer training?
What do you like best about AJAX (ease of use, syntax)? ?What do you like least (debugging, learning curve)?

Be prepared to discuss your experience with AJAX openly and thoughtfully. While these questions are not overly technical in nature, they give the interviewer valuable information regarding your experience and confidence with AJAX, and may even provide insight into how you approach application development.

After you get past these basics, it?s time to pursue the more technical side of the interview.

Top AJAX Interview Questions ? and Answers

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1. Explain the concept of AJAX and its use.

AJAX utilizes CSS, JavaScript, XML, and HTML to exchange data (send and receive) with a server. This information can update a web page without the need to reload the entire page, which makes web pages more interactive and faster.

2. What are advantages and disadvantages of using AJAX?

With a working knowledge of JavaScript, it is fairly easy to utilize AJAX, since JavaScript functions are used to call web services.

PROS

Responsiveness ? AJAX streamlines the transfer of data requests to the server
JavaScript object XMLHttpRequest is used to exchange data with the server asynchronously
AJAX includes options for performing validation and other functions
Ability to update information on the web page without a complete page reload
Open-source JavaScript libraries can be utilized
JavaScript Object Notification (JSON) can be used as an alternative to XML

CONS

Adding another toolset to development activity may increase complexity and extend the development effort
Since AJAX is a client-side function, data security can become an issue
Browsers with JavaScript disabled cannot utilize the application
Other servers cannot be accessed dynamically. AJAX can only exchange data with the server that initiated the web page
Since AJAX exchanges data dynamically, the data will not be available for indexing by search engines, impacting the SEO optimization of the page

3. What is the difference between synchronous and asynchronous AJAX requests?

Synchronous requests wait for a response from the server before proceeding. This can result in a wait for the user of the web application, which is of course not a desirable situation.

Asynchronous processing allows the web page to continue while the request is being processed, such that the browser remains responsive to the client user, allowing the user to perform other functions.

4. Describe how to create an AJAX request, and the process used.

In AJAX, utilize the API XMLHttpRequest to exchange data with the server. The exchange can be in the form of XML, HTML, or JSON. This exchange can both send to and receive data from the server.

Create the request object
Use the open method to open the request
Use the send method to actually initiate the send

AJAX states associated with the request:

request created, not yet open
open method has???? been called
send method called (content headers usually available)
in process ? data is being received but not complete
complete ? request is complete and data available

5. Can you cancel an AJAX request in process?

Yes ? by specifying the abort() method on the request, although there is already a default timeout on each AJAX request. This abort option will stop the client from listening for the event of that AJAX request.

The catch is ? since the request has been sent, the server will likely continue to process the request, since the asynchronous call has already been initiated.C

6. What is AJAX polling?

Since some server data is updated frequently, AJAX polling is a process of regularly retrieving the data from the server to ensure that it is current and available in real-time.

7. What controls are used in AJAX?

AJAX provides these controls:

ScriptManager ? this must be present on the web page for other controls to function
UpdatePanel ? a container control with child controls within it. Triggers that initiate actions within this control cannot impact other portions of the web page
UpdateProgress ? provides information to the client browser while UpdatePanel requests are in progress, such as ?page data loading? or other information useful to the client user
Timer ? timer control initiates automatic post back by setting the triggers property for the UpdatePanel control, or by creating a timer control on the UpdatePanel to serve as a child control directly

8. What is the function of the UpdatePanel?

UpdatePanel controls a specific portion of a web page, functioning as a server control. This control prevents the user from handling outside controls, as UpdatePanel takes over such control, utilizing ScriptManager.

9. How many UpdatePanels can be included within a single web page?

10. What are the differences between JavaScript and AJAX?

Key differences between JavaScript and AJAX include:

AJAX performs asynchronous requests so that other web page functions can continue while the request is being serviced. AJAX is not waiting for a response from the server before continuing with other processes.
JavaScript waits for a response to a request from the server before continuing.
JavaScript manages and controls a web page in its entirety, after the web page has been downloaded.
AJAX does not require a full web page to be reloaded. It can manage and control portions of a web page independently.
JavaScript requires a request to the server for every activity on the page, increasing interaction with the server.
AJAX reduces the server load by making individual requests only for portions of a web page that require updates or information exchange, without a total page reload.

11. What tools and technologies does AJAX utilize?

AJAX utilizes a variety of functional technologies:

JavaScript ? this is a key requirement of AJAX development
XMLHttpRequest ? utilized to communicate with the server
DOM ? for content management
HTML/XHTML ? providing the documents to the application
CSS ? for managing document attributes including fonts, colors, and more

12. What is JSON, and how is it used in AJAX?

JSON stands for JavaScript Object Notation. It is the interchange format utilized in JavaScript to exchange data safely and reliably.

13. Are there any scenarios where AJAX should not be used?

Due to the dynamic nature of how AJAX will populate portions of web pages, AJAX may not be the best choice where SEO is a primary concern. Browsers that do not support JavaScript are not suitable for AJAX development, since JavaScript is the foundation for AJAX.

Since AJAX is populating and updating data on the server through its interaction with web pages in real time, applications where data security is essential are not the most suitable for AJAX development.

14. How do you manage exceptions in AJAX?

ScriptManager includes the ErrorTemplate tag which can be used to manage any exception processing required.

15. How can you perform unit tests and debugging in AJAX applications?

JsUnit is the client-side tool used for unit testing JavaScript code. It can also be utilized for testing AJAX code. In addition, there are commercial testing and debug platforms available specifically for testing JavaScript and AJAX applications:

Fiddler for Internet Explorer
Firebug for Mozilla
Postman
JS Bin

?After the Interview

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You may not get the first AJAX development position you interview for, but preparation is key to making the right impression on the interviewer and having the right answers to each question.

Certainly, you will not have the answer for every AJAX interview question on the tip of your tongue, so after the interview, you should think in terms not only of this interview, but of the next one.

What questions took you a bit off-guard or were totally outside your experience level? Note those questions for follow-up and be prepared with the answers for the next position you interview for.

Follow up with the interviewer within the next 24-48 hours to thank them for their time and for considering you for the position. Be sure to confirm your interest in the job. Good luck with your search for an AJAX development position.