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Ajax interview question


1) What is AJAX?

AJAX stands for Asynchronous JavaScript and XML. It is a group of related technologies used to display data asynchronously. In other words, it sends and retrieves data without reloading the web page. 

2) What are the advantages of AJAX?

  • Quick Response
  • Bandwidth utilization
  • The user is not blocked until data is retrieved from the server.
  • It allows us to send only important data to the server.
  • It makes the application interactive and faster.

3) What are the disadvantages of AJAX?

  • Dependent on JavaScript
  • Security issues
  • Debugging is difficult

4) What are the real web applications of AJAX currently running in the market?

  • Twitter
  • Facebook
  • Gmail
  • Javatpoint
  • Youtube

5) What are the security issues with AJAX?

  • AJAX source code is readable
  • Attackers can insert the script into the system

6) What is the difference between synchronous and asynchronous requests?

Synchronous request blocks the user until a response is retrieved whereas asynchronous doesn't block the user. 

Synchronous Request

Asynchronous Requestasynchronous request

7) What are the technologies used by AJAX?

  • HTML/XHTML and CSS - These technologies are used for displaying content and style.
  • DOM - It is used for dynamic display and interaction with data.
  • XML - It is used for carrying data to and from server
  • XMLHttpRequest - It is used for asynchronous communication between client and server.
  • JavaScript - It is used mainly for client-side validation

8) What is the purpose of XMLHttpRequest?

  • It sends data in the background to the server.
  • It requests data from the server.
  • It receives data from the server.
  • It updates data without reloading the page.

9) What are the properties of XMLHttpRequest?

The important properties of the XMLHttpRequest object are given below.
  • onReadyStateChange - It is called whenever readystate attribute changes.
  • readyState - It represents the state of the request.
  • responseText - It returns response as text.
  • responseXML - It returns response as XML.
  • status - It returns the status number of a request.
  • statusText - It returns the details of status.

10) What are the important methods of XMLHttpRequest?

  • abort() - It is used to cancel the current request.
  • getAllResponseHeaders() - It returns the header details.
  • getResponseHeader() - It returns the specific header details.
  • open() - It is used to open the request.
  • send() - It is used to send the request.
  • setRequestHeader() - It adds request header.

11) What are the types of open() method used for XMLHttpRequest?

  • open(method, URL) - It opens the request specifying get or post method and URL.
  • open(method, URL, async) - It is same as above but specifies asynchronous or not.
  • open(method, URL, async, username, password) - It is same as above but specifies the username and password.

12) What are the types of send() method used for XMLHttpRequest?

  • send() - It sends get request
  • send(string) - It sends post request.

13) What is the role of the callback function in AJAX?

The callback function passes a function as a parameter to another function. If we have to perform various AJAX tasks on a website, then we can create one function for executing XMLHttpRequest and a callback function to execute each AJAX task.

14) What is JSON in AJAX?

JSON stands for JavaScript Object Notation. In AJAX, it is used to exchange data between a browser and a server. It is easy to understand, and data exchange is faster than XML. It supports array, object, string, number, and values.
  1. request.onreadystatechange  = function(){    
  2.       if (request.readyState == 4  )    
  3.       {    
  4.         var jsonObj = JSON.parse(request.responseText);//JSON.parse() returns JSON object    
  5.         document.getElementById("date").innerHTML =  jsonObj.date;    
  6.         document.getElementById("time").innerHTML = jsonObj.time;    
  7.       }    
  8.    } 

15) What are the tools for debugging AJAX applications?

There are several tools for debugging AJAX applications.
  • Firebug for Mozilla Firefox
  • Fiddler for IE (Internet Explorer)
  • JavaScript HTML Debugger
  • MyEclipse AJAX Tools
  • Script Debugger

16) What are the types of post back in AJAX?

There are two types of post back in AJAX.
  • Synchronous Postback - It blocks the client until the operation completes.Asynchronous Postback - It doesn?t block the client.

17) What are the different ready states of a request in AJAX?

There are 5 ready states of a request in AJAX.
  • 0 means UNOPENED
  • 1 means OPENED
  • 2 means HEADERS_RECEIVED
  • 3 means LOADING
  • 4 means DONE

18) What are the common AJAX frameworks?

  • Dojo Toolkit
  • YUI
  • Google Web Toolkit (GWT)
  • Spry
  • MooTools
  • Prototype

19) How can you test the AJAX code?

JUnit is the open source unit testing framework for client-side JavaScript. It is required to create test cases. The unit test case is a code which ensures that the program logic works as expected.

20) What is the difference between JavaScript and AJAX?

JavaScript is an object-based scripting language.AJAX is a group of inter-related technologies like JavaScript, XML, HTML, CSS etc
It requests the server and waits for the response.It sends a request to the server and doesn't wait for the response.
It consumes more bandwidth as it reloads the page.It doesn't reload the page so consumes less bandwidth