2021 Top jQuery Interview Questions - Interviewbit IQCode

JQuery Interview Questions

Below are some commonly asked interview questions related to JQuery:

  // example code here

Make sure to review the JQuery documentation and practice implementing different JQuery methods and functions to improve your understanding and skills.

Overview of jQuery JavaScript Library

jQuery is a widely used, open-source, lightweight JavaScript library designed to simplify the interaction between HTML, CSS documents and JavaScript. It was primarily created to make interactions between Document Object Model (DOM) and JavaScript, more straightforward. jQuery also simplifies the use of commonly practiced JavaScript functionalities that required multiple lines of code, into a single line and also assists in performing AJAX calls with ease.

Some noteworthy features of jQuery include:

  • DOM manipulation and traversal
  • Event handling
  • Cross-browser support
  • CSS manipulation
  • AJAX support
  • Animation and effects

//example to showcase jQuery features
//hide all paragraph elements

//on button click, show all paragraph elements

JQuery Interview Questions:

1. Describe jQuery?

2. What are the benefits of using jQuery?

3. Is jQuery a JavaScript or JSON library file?

4. Does jQuery support both XML and HTML documents?

5. What are the jQuery functions used to create effects?

6. What is the purpose of the css() method in jQuery?

7. Define events in jQuery?

8. What is the purpose of jQuery.length?

9. Explain jQuery click event?

10. Can you explain about the jQuery each() method?

11. What is the difference between JavaScript and jQuery?

12. What are the selectors in jQuery? How many types of selectors are available in jQuery?

13. How can CSS classes be manipulated in HTML using jQuery?


// jQuery code snippet to manipulate CSS classes in HTML

// remove class 'example' from div element with ID 'container'

// add class 'example' to div element with ID 'container'

// toggle class 'example' on button click event
$('#myButton').click(function() {

JQuery Interview Questions

In this section, you will find JQuery interview questions related to AJAX requests, code snippets, and methods to manipulate elements in jQuery.

1. How to perform AJAX requests using jQuery?


method can be used to perform AJAX requests in jQuery. It allows specifying various parameters such as URL, request type, data, success/failure callbacks, and more.

2. What does the following code do?

The following code selects all


elements in the form with ID


and sets their


attribute to empty string:

$('#myForm input').val('');

3. Consider the following code that exists in HTML:

<script src="https://code.jquery.com/jquery-3.3.1.min.js"></script>

This code adds the jQuery library to the HTML page, allowing the usage of jQuery methods and functions.

4. What does the following code do?

The following code selects all


elements that have the class


, and attaches a click event listener to them that hides the selected elements:

$('div.foo').on('click', function() { $(this).hide(); });

5. Can you explain the difference between





is a shorthand method for making GET requests to the server, while


is a more flexible method that can be used to make requests with any HTTP method (GET, POST, PUT, DELETE, etc.) and allows more fine-grained control over the request.

6. Which of the two lines of code below is more efficient and why?


The second line of code is more efficient because it uses native JavaScript methods, which are generally faster than querying the DOM with jQuery.

7. Can you write a jQuery code selector that needs to be used for querying all elements whose ID ends with the string “IB”?


This selector uses the attribute ends with selector


to select all elements whose ID ends with the string



8. Explain the

method in jQuery.


returns a Promise object that can be used to handle asynchronous operations in jQuery. It takes an optional argument that specifies which set of actions to create a Promise for (e.g. animation or AJAX), and can be used to perform actions such as .done(), .fail(), and .always().

9. Consider the below code snippet and assume that there are 5 elements on the page. What is the difference between the start and end times displayed?

$('div').each(function() {
  // do something

The difference between the start and end times displayed is the time taken to execute the


function on all 5


elements on the page.

10. Can you tell the difference between





is used to get or set properties of DOM elements such as checked and selected, while


is used to get or set attributes of DOM elements such as href and src. In general, it is recommended to use


for boolean properties and


for other attributes.

Introduction to jQuery

jQuery is an open source library that simplifies interactions between JavaScript and the Document Object Model (DOM). It is one of the most popular libraries used for front-end web development.

Advantages of using jQuery

jQuery is a popular open-source library that provides several benefits when used for web development:

  • jQuery is popular and open source, making it easy to find community support and resources.
  • jQuery is fast and easily extendable, allowing developers to create complex applications quickly.
  • With jQuery, developers can create cross-browser compatible web applications as it works similarly across different browsers.
  • Using the minified version of the jQuery library improves application performance by reducing the file size by almost 50%. This helps web pages load faster.
  • jQuery provides pre-written UI functionalities with minimal lines of code, making it easier for developers to focus on other aspects of development.
//using jQuery to select DOM elements

Overall, jQuery simplifies the development process and enhances the user experience of web applications.

Understanding jQuery as a JavaScript Library

jQuery is a JavaScript library that contains a single file. This file provides DOM/CSS manipulations, event effects or animations, AJAX functions, and various commonly used plugins. jQuery is not a JSON library file.

Does jQuery work for both HTML and XML documents?

No, jQuery only works for HTML documents.

// jQuery code example
$(document).ready(function() {
  // code here

What are the jQuery Functions used to Provide Effects?

jQuery provides various methods to apply effects on HTML elements. Some of these methods are:

  • toggle()

    : This function is used to check the visibility of selected elements and toggle between hiding them using


    and showing them using


    . When the element is hidden, the


    function is run, and vice versa. The syntax for this method is

    $(selector).toggle(speed, easing, callback)


  • slideDown()

    : This function is used to check the visibility of selected elements and show the hidden elements using a sliding animation effect. This function can be used on elements that are hidden using jQuery methods or that use the

    display: none

    property in the element’s CSS properties. The syntax for



    $(selector).slideDown(speed, easing, callback)


  • fadeOut()

    : This function is used to reduce the level of opacity of an element of choice from visible to hidden. When used, the faded element will not occupy any space in the Document Object Model (DOM). The syntax for



    $(selector).fadeOut(speed, easing, callback)


  • fadeToggle()

    : This function is used to toggle between the




    methods. If the elements are in a faded-in state,


    will fade out those elements. If elements are faded out,


    will fade in those elements. The syntax for



    $(selector).fadeToggle(speed, easing, callback)


  • animate()

    : This method performs custom animation of a set of CSS properties. It changes an element from one state to another with CSS styles, gradually changing the CSS property value to create an animated effect. The syntax for



    $(selector).animate({styles}, speed, easing, callback)

    , where the "styles" parameter is a required field that specifies one or more CSS properties/values to animate. The properties need to be mentioned in camel case style.

The parameters "speed", "easing", and "callback" in the syntaxes of the above methods are optional. "Speed" specifies the speed of the effect. The default value is 400 milliseconds, and may be set to "slow", "fast", or some number in milliseconds. "Easing" is used to specify the speed of the element to different types of animation. The default value is "swing", and may be set to "swing" or "linear". "Callback" is an optional parameter, and the callback function specified here is executed after the effect method is completed.

Explanation of the jQuery CSS() Method

The jQuery


method is utilized to modify the style properties associated with the chosen element. It is employed to update the CSS properties of an HTML element dynamically. This method is valuable when it comes to designing responsive web pages in which the style properties of HTML elements change dynamically based on the user's input or device parameters.

Understanding Events in jQuery

In web development, events refer to user actions on a webpage, such as clicking a button or pressing a key on the keyboard. Handling responses to those actions is called event handling.

jQuery, a popular JavaScript library, simplifies event handling by providing easy-to-use methods for attaching event handlers to selected HTML elements. When an event occurs, the function that is attached to it is executed.

To attach an event handler using jQuery, you can use the following syntax:

$(selector).on(event, function);

Here, the selector identifies the HTML element(s) you want to attach the event handler to, and the event specifies the user action that triggers the handler (e.g. "click" or "keydown"). The function is the code that is executed when the event occurs.

Understanding the significance of jQuery.length

The jQuery.length property serves the purpose of counting the number of elements present in the jQuery object.


Consider the following code:

var elements = $("p"); 

In this case, the elements variable stores all the <p> tags present in the DOM.


The code above will output the count of all the <p> tags present in the DOM.

Thus, jQuery.length is an important property that enables developers to retrieve the number of elements from a jQuery object.

Understanding the jQuery Click Event

The jQuery click event is triggered when we click on an HTML element. To assist in triggering this event, jQuery provides the click() method. For instance, if we want to trigger a click event whenever a paragraph element is clicked on, we can use the following syntax: $(“p”).click().

Here is the syntax for setting up a click event handler:

  // code that runs when the click event is triggered

The `selector` means the HTML element or elements we want to attach the click event to, and the function defines the actions we want to take when the click event occurs.

Understanding the Each() Method in jQuery

The each() method is a powerful tool in jQuery that allows you to iterate through datasets like arrays and objects, even the DOM objects. It can be used to select multiple DOM objects from the same selector and loop through them. For instance, to add the width '600' to all images in a page, we can select and loop through all images and add the attribute using the following code:


In the code above, "$" is a jQuery object definer. The "this" inside the function represents a DOM object. Since we can only apply jQuery functions to jQuery objects, we need to wrap the DOM object inside the $ definer to convert it to a jQuery object and then apply jQuery functions to it.

We can also use the each() method to loop through arrays of data to obtain the index and value of the position of data inside the array. For example,

var list = ["IQCode", "jQuery", "Questions"];
$.each(list, function(index, value){
    console.log(index + " " + value);

Running the above code will produce the following output: 0 IQCode 1 jQuery 2 Questions

Similarly, we can use the each() method to loop through objects using the following code:

var obj = {"name":"IQCode","type": "jQuery"};
$.each(obj, function(key,value){
    console.log(key + " - " + value);

Running the above code will produce the following output: name - IQCode type - jQuery

Differences between JavaScript and jQuery

JavaScript is an interpreted language that combines ECMAScript and DOM, written in C. On the other hand, jQuery is a JavaScript library designed to simplify and speed up JavaScript performance. Given below are some of the key differences:

  • jQuery doesn't have a separate version of ECMAScript, unlike JavaScript.
  • JavaScript requires longer lines of code to create functionality while jQuery provides pre-built functions that can be called by simply importing the library, thus saving the programmer's coding effort.
  • As compared to JavaScript, jQuery has built-in cross-browser compatibility functionality that saves developers the effort of coding them manually.
// Example:
// JavaScript code
document.getElementById('myElement').addEventListener('click', function(){
  alert('Hello, World!');
// jQuery code
  alert('Hello, World!');

Types of Selectors in jQuery

In order to manipulate elements on a webpage, it's important to first be able to select them using jQuery. jQuery provides various types of selectors to match our needs. Here are some of the most commonly used types of selectors:

  // Name Selector: selects all elements that match the given element name
  // ID Selector: selects a single element that matches the given ID
  // Class Selector: selects all elements that match the given class
  // Universal Selector: selects all elements on the page
  // Multiple Selector: selects the combined results of all the specified selectors
  $('E, F, G')
  // Attribute Selector: selects elements based on the value of their attributes

By utilizing these different selectors, we can easily target and manipulate the desired elements on a webpage using jQuery.

Manipulating CSS Classes in HTML using jQuery

jQuery provides several methods to manipulate the CSS classes assigned to HTML elements. The most common methods are addClass(), removeClass() and toggleClass().

addClass(): This method adds one or more classes to the selected elements.

Syntax: $(selector).addClass(className);

You can also add multiple classes to the selector.

Syntax: $(selector).addClass(class1, class2);

removeClass(): Similar to adding class, you can also remove the classes from the elements by using this method. The removeClass() method can remove a single class, multiple classes, or all classes at once from the selected elements.


  • For removing one class: $(selector).removeClass(class1);
  • For removing multiple classes: $(selector).removeClass(class1, class2, class3);
  • For removing all classes at once: $(selector).removeClass();

toggleClass(): This method is used for adding or removing one or more classes from the selected elements. If the selected element already has the class, then it is removed. Otherwise, if an element does not have the specified class, then it is added, i.e., it toggles the application of classes.

Syntax: $(selector).toggleClass(className);

How to Make JQuery AJAX Requests

JQuery provides a method called


to make an asynchronous HTTP request. You can use the following syntax:

$.ajax({name:value, name:value, ... });

You can specify one or more name-value pairs for the parameters. Below are the names that you can use:

  • url

    - specifies the URL to send the request to. The default is the current page.

  • success(result,status,xhr)

    - A callback function that runs when the request succeeds.

  • error(xhr,status,error)

    - A function that runs if the request fails.

  • async

    - A Boolean value that indicates whether the request should be handled asynchronously or not. The default value is true.

  • complete(xhr,status)

    - A function that runs when the request is completed (after success and error functions are handled).

  • xhr

    - A function used for creating the XMLHttpRequest object.

Here's an example:

  url: "resourceURL",
  async: false,
  success: function(result){
  error: function(xhr){
    alert("An error occurred: " + xhr.status + " " + xhr.statusText);

Explaining a jQuery Selector

The given code demonstrates a jQuery selector that retrieves multiple elements satisfying specified selectors. The result is a jQuery object that contains the selected elements.

In particular, the code searches for:

  • An element with ID "firstDiv" having tag name "div"
  • All elements that have class "firstDiv" and tag name "div"
  • All elements that are direct children of an ordered list (OL) with ID "items" and whose name attribute ends with the string "firstDiv"

The jQuery library is used to simplify the process of finding and manipulating HTML elements. The selector syntax is similar to that of CSS, with some differences. The result of the selector operation depends on the structure and content of the document being searched.

$( "div#firstDiv, div.firstDiv, ol#items > [name$='firstDiv']" )


This is some code for practicing jQuery interview questions.

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