AJAX Interview Questions

A list of frequently asked AJAX interview questions and answers are given below.

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. More details.

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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.

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3) What are the disadvantages of AJAX?

• Dependent on JavaScript
• Security issues
• Debugging is difficult

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

• Twitter
• Facebook
• Gmail
• Javatpoint
• Youtube

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5) What are the security issues with AJAX?

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

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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. More details.

Synchronous Request

Asynchronous Request

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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

More details.

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8) What is the purpose of XMLHttpRequest?

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• 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.

More details.

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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.

More details.

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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.

More details.

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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.

More details.

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

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

More details.

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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.

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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.    }  

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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

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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.


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• Asynchronous Postback - It doesn?t block the client.

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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

More details.

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18) What are the common AJAX frameworks?

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

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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.

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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.