jQuery Interview Questions and Answers

What is jQuery?

jQuery is an open source JavaScript library that simplify Html document traversing and manipulation browser event handling, DOM animations, Ajax interaction and cross bowser JavaScript development.

How jQuery differ from JavaScript?

jQuery is just a JavaScript library and has built in JavaScript code functionality that optimized development, reduce effort and provided cross browsers supports.

Why jQuery and features of jQuery?

jQuery philosophy is “Write less, do more”

Open source and has large community of users and contributors

Tested and optimized for modern browsers

Lightweight, robust and expandable

Offers plug-ins and ready-made functionality

Can be used for event-driven programming

AJAX support

How we can use jQuery on a web page?

We can use jQuery in web page by two way

Use of content delivery network (CDN) to include a version of jQuery.
Downloaded version of jQuery in local file-system from jQuery.com.

What is a CDN? Why a CDN is Useful to jQuery and advantage of it?

Content delivery network is geographically distributed worldwide high-speed collection of servers, which can serve content to end-users in lowround-trip times.

Advantage:

We can start using jQuery from CDN simply by adding a <script> tag in web page without locally downloaded.

Browsers reused cached jQuery files for web sites that are located in different domains, which significantly improve performance.

CDN offers reliable high-speed access on jQuery library withminimum round-trip time.

Which are the popular jQuery CDN? How to load jQuery from CDN?

Google, Microsoft and jQuery are popular jQuery CDN.

To load a hosted library from CDN, copy and paste the below HTML snippet for that library (shown below) in your web page

Google (https://developers.google.com/speed/libraries/#web-font-loader)
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.3/jquery.min.js"></script>

Microsoft (http://www.asp.net/ajax/cdn)
<script src="http://ajax.aspnetcdn.com/ajax/jquery/jquery-1.9.0.min.js"></script>

JQuery (https://code.jquery.com/)
<script src="http://code.jquery.com/jquery-1.9.1.min.js"></script>

How to load jQuery locally when CDN unavailable?

To allow to loading jQuery from a local path on your own website if the CDN happens to be unavailable, add the following element immediately after the element referencing the CDN:

<script src=" /jquery/jquery-1.9.0.min.js"></script>

Ex:

<script src="http://ajax.aspnetcdn.com/ajax/jquery/jquery-1.9.0.min.js"></script>

<script src=" /jquery/jquery-1.9.0.min.js"></script>

What is the difference between jQuery and its alias $?

jQuery and $ are the same thing and work same. $ is just a shortcut.

For example, the following statement will create an <a>element wrapped inside of a <p>element with a text node encapsulated inside of the <p>and <a>elements:

jQuery('<p><a>jQuery</a></p>');
which is the same as
$('<p><a>jQuery</a></p>');

Can we replace any character or variable instead of $ in jQuery?

We can replace $ by using no Conflict () method, see below snippet to replace $ to jqwrite

var jqwrite = $.noConflict()

Explained jQuery document.ready() function?

Everything inside the $(document).ready() function will load as soon as the DOM (Document Object Model) is loaded and before the page contents are loaded.

The ready() event handler method is jQuery’s replacement for using the JavaScript core window.onloadevent.

jQuery Document Ready Snippet
$(document).ready(function() {  // Put javascript here});

Different ways to write jQuery Document Ready Snippet
$(document).ready(function() { ... });
$(function() { ... });
jQuery(document).ready(function() { ... });
jQuery(function() { ... });

jQuery document ready function can be used as many times in page as you like.

What is the difference between JavaScript window.onload() event and jQuery ready()functions?

jQuery ready() function only waits for the DOM tree to be loaded before executing the code. Where JavaScript onload event not only waits for DOM to be created but also waits for all external resources to load fully including heavy images, audios and videos etc.
If loading images and other third party elements takes significant amount of time then user can experience significantly be impacted on execution of code defined in window.onloadevent.

As mentioned above jQuery ready() function recommended over JavaScript onload event. However, there are valid use cases that justifies use of JavaScript onload over jQuery ready().

What are selectors in jQuery and how many types of selectors are there?

jQuery selectors are used to select html elements to in order to operate on the element based on their id, class, element type, attributes, and many more. There are many types of selectors but important selectors are:

Element Selector (“element”):Selects all elements with the given tag name
$(“div”).css(“color”,”red”);// text color of all div elements will be red

All Selector (“*”): select all HTML elements at a time.
$(“*”).css(“color”, “blue”);//change all elements text color to blue

Id Selector (“#id”): Selects a single element with the given id attribute.
$(“#id”).css(“background”, “black”);

Class Selector (“.class”): Selects all elements with the given class.
$(“.class”).css(“color”, “black”);

Attribute Selector [name=”value”]: Select elements based on its attribute value.

Multiple Selector (“selector1, selector2, selectorN”): Select elements that match all selector condition.

Latest Updates

Trigonometry

What is the value of cot 4π/3 ?

Indian Politics

Article-24 of the Indian Constitution ‘Prohibition of employment of children in factories, etc’ deals with?

Article-134A of the Indian Constitution ‘Certificate for appeal to the Supreme Court’ deals with?

Chemistry

Who invented Aspirin?

Physics

A larger force on a rotating body results in larger?

What is the unit of the physical quantity, magnetic flux density?

Algebra

The system of equations 2x + 4y = 6 and 4x + 8y = 8 is ?

Time and Distance

A thief is spotted by a policeman from a distacne of 100 m. When the policeman starts the chase, the thief also starts running. If the speed of the theif is 8 km / hour and that of the policeman is 10 km/hour, then how far will the theif have to run before he is overtaken?

Algebra

Aman and Alok attempted to solve a quadratic equation. Aman made a mistake in writing down the constant term and ended up in roots (4, 3). Alok made a mistake in writing down the coefficient of x to get roots (3, 2). The correct roots of the equation are?

Compound Interest

The effective annual rate of interest corresponding to a nominal rate of 22% per annum payable half-yearly is?

Volume and Surface Area

If the volume of a cylinder is 2156 cubic cm and height is 14 cm, find its radius?

Algebra

What is the equation of the line which passes through the points (2, 3) and (- 4, 1)?

Triangles

In △ABC, the angle bisector of ∠A cuts BC at E. Find length of AC, if lengths of AB, BE and EC are 9 cm, 3.6 cm and 2.4 cm?

In a triangle, the length of the opposite side of the angle which measures 45° is 8√2 cm, what is the length of the side opposite to the angle which measures 90°?

General Knowledge of India

The boundary line between India and Pakistan is called?

Which city is located on the banks of the river Mahanadi?

Indian History

When was the battle of Haldighati fought?

In 1498, which Portuguese explorer discovered a new sea route from Europe to India?

General Knowledge of India

Chapchar Kut is a festival of which State?

Chemistry

In chemistry, soap is a salt of a ?

Indian Economy

Which of the following is a Direct tax?

Biology

Sauria lacertidae is the scientific name of?

Which of the following is a primary function of haemoglobin?

Average

A factory buys 8 machines.3 Machine A, 2 Machine B and rest Machine C. Prices of the machines are 100000, 80000 and 45000 respectively.Calculate the average cost of these machines?

Discount

Ticket for an adult is 500 and a child is 200. 1 child goes free with two adults. If a group has 20 adults and 8 children what will be the discount the group get?