Ajax interview questions
AJAX or Asynchronous Javascript and XML is one of the most preferred platforms used by developers. We also find its application in several industries and verticals as it offers unique features. A lot of brands hire developers who can work on this platform so that they can get their websites designed on it. The platform seems promising as it can build interactive web applications, which are required for retaining the visiting customer and engaging them for a longer duration. This is one of the factors that increases the page ranking on SERP.Today the demand for the AJAX developers has increased and corporate houses and business owners are looking forward to hire them. Almost every organization is trying to hold up a strong social presence and therefore developers are hired to make the presence even stronger among the potential customers. The interview for the developers can be tough as the competition is really high and the market is full of talent. While some prefer general knowledge on programming other interviewers can ask technical questions.Thus, here is a list of compiled possible Ajax interview questions that can be asked by an interviewer:
1.Brief about Ajax.
Ajax is considered to be a developer’s best friend because it offers several benefits to him such as updating the web page without reloading the entire page, requesting data from the server and also sending data to the server. AJAX is the acronym for Asynchronous JavaScript and XML. It is a new technique to communicate to and from a server/ database without completely refreshing the page. It creates faster, interactive, better web applications with help of CSS, XML, HTML, and JavaScript.
2.Differentiate between Synchronous and Asynchronous Ajax requests.
Synchronous Ajax requests– In this, the script stops and waits for the server to reply before continuing. In web application world, one has to happen after the other, i.e. the interaction between the customer and the server is synchronous. Synchronous is not recommended as it blocks/hangs the page until the response is received from the server.
Asynchronous Ajax requests handle the reply as and when it comes and allows the page to continue to be processed. Under Asynchronous, if there is any problem in the request it can be modified and recovered. The request doesn’t block the client as the browser is responsive. The user can perform other operations as well.
3. List some advantages and disadvantages of using Ajax.
Ajax is a very easy concept if one has a sound knowledge of JavaScript. It uses JavaScript functions to call methods from a web service. It has certain advantages-
- Speed- Ajax reduces the server traffic and also the time consumption on server and client side.
- Ajax is very responsive and fast, data can be transferred at a time.
- XMLHttpRequest plays a significant role in Ajax. It is a special JavaScript object that calls asynchronous HTTP request to the server for transferring data.
- One of the biggest advantages of using Ajax as forms are common elements in the web page. Ajax gives options for validation and much more.
- One doesn’t have to completely reload the page.
There are some disadvantages attached to Ajax. They are-
- Search engines would not be able to index Ajax applications so Ajax maybe a mistake.
- Anyone can have access to the code of Ajax and can view source it.
- ActiveX requests are enabled only in internet explorer and other new browsers.
4. What are different readyState in Ajax.
There are total 5 ready state in Ajax:
| Value | State | Description |
|---|---|---|
| 0 | UNSET | Client has been created. Open() not yet called. |
| 1 | OPENED | Open() called. |
| 2 | HEADRERS_RECIEVED | Send() called and headers are available. |
| 3 | LOADING | Downloading: responseText holds partial data. |
| 4 | DONE | The operation is complete. |
5. What is XMLHttpRequest object in Ajax? How can you XMLHttpRequest Object?
The XMLHttpRequest objects are used to exchange data with a server. It is an API whose methods transfer between a web browser and a web server. In XHR, it’s not necessary that data have to be in form of XML. It can be JSON or HTML. XHR can be used with protocols other than HTTP.
XMLHttpRequest is any developers kit because it has the option to update the page without reloading the entire page. You can request data from the server and also send data to the server in the background.
6. How to cancel the current request in Ajax?
Current request in AJAX is cancelled when the user performs an action which sets of an Ajax request. This can be depicted with the help of auto-complete functionality for a search box where users can be helped with related search terms based on their current input, by making an AJAX request each time they pass a key in search field. The user types faster than the Ajax request and you would want to abort any non-finished requests, before starting the next one.
7. How to send an Ajax request in JavaScript?
HTTP Requests are created with the help of XMLHttpRequest objects. It facilitates the transfer of data between client and server which happens via request and response. In XMLHttpRequest, you can perform the same function plus you can grab data from URL without having to refresh the page. AJAX lets you perform actions without reloading the entire page. The following steps tell how to call AJAX-
- Create an XMLHttpRequest object.
- Open the request with open method.
- Now, send the request with the send method.
8. Explain Fetch API in JavaScript.
Fetch API uses to request and response objects that can be used in future whenever needed. It provides an interface for fetching resources. Fetch API uses promises that enable cleaner API. Cache API or other similar things handles the request and responses that might require you to generate your own responses programmatically.
Thus, you can now crack your interview and work as a developer in one of your dream companies by preparing from these set of question and answers to be technically sound.
9. Explain limitations of Ajax.
1)Browser Integration
The dynamically created page does not register itself with the browser history engine, so triggering the “Back” function of the users’ browser might not bring the desired result.
2)Response-time Concerns
Network latency – or the interval between user request and server response – needs to be considered carefully during Ajax development.
3)Search Engine Optimization (SEO)
Websites that use Ajax to load data which should be indexed by search engines must be careful to provide equivalent Sitemaps data at a public, linked URL that the search engine can read, as search engines do not generally execute the JavaScript code required for Ajax functionality.
4)Reliance on JavaScript
Ajax relies on JavaScript, which is often implemented differently by different browsers or versions of a particular browser. Because of this, sites that use JavaScript may need to be tested in multiple browsers to check for compatibility issues.
10. Explain what is polling in AJAX.
The Process of retrieving data from a server to obtain near-live data regularly is called AJAX polling.
