jQuery Interview Questions and Answers

Master the art of jQuery with 'jQuery Interview Questions and Answers.' This blog is your ultimate resource for preparing for jQuery-related interviews, featuring a comprehensive collection of questions and detailed answers. Whether you're a front-end developer, a web designer, or a jQuery enthusiast, our guide delves into jQuery essentials, DOM manipulation, event handling, and best practices. Prepare with confidence and explore the world of efficient client-side scripting with jQuery.

1. What is jQuery?

jQuery is a fast and lightweight JavaScript library that simplifies HTML document traversal and manipulation, event handling, animation, and AJAX interactions.

2. Explain the difference between `$(document).ready()` and `$(window).load()`.

`$(document).ready()` is triggered when the DOM is fully loaded, while `$(window).load()` is triggered when all assets (including images) have been loaded.

3. What are the advantages of jQuery?

4. List some Features of jQuery.

jQuery includes the following features:

5. Is jQuery a JavaScript or JSON library file?

jQuery is said to be a library of single JavaScript files which consists of DOM/CSS manipulations, event effects or animations, AJAX functions and various commonly used plugins.

6. Does jQuery work for both HTML and XML documents?

No. jQuery works only for HTML documents.

7. What is jQuery Mobile?

Query Mobile is a JavaScript library that enables developers to create mobile-first applications. It is a lightweight framework that allows developers to create rich, touch-first interfaces that are optimized for touch devices.

jQuery Mobile is a mobile-first JavaScript library that aims to provide a modern and easy-to-use framework for developing mobile apps. It was originally developed by Facebook to improve the performance of its iOS and Android apps. Since then, it has been adopted by many other companies, including Google, Yahoo, and Mozilla.

When using jQuery Mobile, you can use the library to create a mobile-first app that is faster and easier to maintain than traditional web apps. It also makes it easier to add new features to your app without having to rewrite your code.

JQuery Mobile is built on top of the jQuery JavaScript library. It works by using the same techniques that are used when you are developing a traditional web app. However, instead of using JavaScript, jQuery Mobile uses HTML5 and CSS3 to create a modern and easy-to-use framework for developing mobile apps.

8. What is the $() function in the jQuery library?

$(document).ready(function() {     $("h1").css("background-color", "green");  });

9. Explain $(document).ready() function?

The $(document).ready() function is a jQuery extension that allows you to immediately run code when the document is ready. It's most commonly used to initialize a new page or to load scripts or styles into the document. However, it can also be used to load a script or style into the document at any time. 

The $(document).ready() function is useful for loading scripts or styles into the document at any time. It's not useful for loading scripts or styles into the document when the document is already loaded.

10. What is the exact difference between the methods onload() and document.ready()?

The onload() and document.ready() methods are used to load and render the HTML and JavaScript code that is needed to display the page.  However, they are different methods in that they use different approaches to loading the HTML and JavaScript code. The exact differences are -

onload() document.ready()
The onload() method is used to load the HTML code. The document.ready() method is used to load the JavaScript code.
The onload() method loads the HTML code using a pre-compiled object that is passed to the onload event handler The document.ready() method loads the JavaScript code using a pre-compiled object that is passed to the document.ready event handler.

11. Describe jQuery Connect in brief. Also, list its uses.

JQuery connect is a JavaScript library that provides a declarative API for binding data to elements. It allows you to specify the data source, the element that should be bound to the data, and the callback function that will be invoked when the element is bound. 

The most common use case for jQuery connect is binding data to an element using an attribute or value. However, it can also be used to bind data to elements dynamically or to bind data to an element based on a condition.

12. What are the jQuery functions used to provide effects?

Some of the methods are listed below which provide the effect:

1. toggle() :

2. slideDown() :

3. fadeOut():

4. fadeToggle():

5. animate():

13. What is the use of css() method in jQuery?

The css() method is used to change the style property of the selected element.

14. Which jquery method is used to hide selected elements?

15. What are events in jQuery?

User actions on a webpage are called events and handling responses to those is called event handling. jQuery provides simple methods for attaching event handlers to selected elements. When an event occurs, the provided function is executed.

16. How to iterate/loop through all p elements in jquery.

$.each() is an object iterator tool provided by jQuery, as is.each(), a jQuery collection iterator(). So for traversing all the p elements, the sample code is - 

$("p").each(function() {    console.log( $(this).attr('id')); });

17. What is the significance of jQuery.length?

jQuery.length property is used to count the number of the elements of the jQuery object.

18. What is jQuery click event?

Syntax:

$(selector).click(function(){ //code that runs when the click event is triggered});

19. What is the purpose of JQuery's delay() method? Can you use this for different types of browsers like (Internet Explorer)?

The delay() method is used to set the delay between two events, such as a click or a change in state. The delay can be set to a number of different values, including milliseconds, seconds, and even hours. This can be useful when you want to wait for an event to occur before doing something else. 

For example - you could use a delay of 5 minutes to wait for a user to click on your button before moving on to the next step in your workflow.

Although the delay() method is not available in all browsers. In order to use it in Internet Explorer, you will need to add the following line of code: 

window.addEventListener('click', function() { delay(5000); });

But the latest Microsoft browser (Microsoft Edge) that replaces the internet explorer has support for the jQuery delay() method.

In addition, the delay() method is not available in some browsers, such as Firefox and Safari. To work around this issue, you can use the setTimeout() method instead.

20. Can you explain about ajaxStart() functions?

The ajaxStart() event is a global event that occurs when an Ajax request begins, assuming no other Ajax requests are presently active. The ajaxStart() event can also be used to cancel a previously called Ajax callback or to start a new one.

For example, suppose you have an online shopping cart application that allows customers to add items to their shopping cart when they are ready to checkout. An ajaxStart() event could be used to trigger a shopping cart initialization routine when the user first visits the application, or any time a new shopping cart is about to be initialized.

Similarly, a shopping cart termination routine could be triggered when the user is finished shopping, or whenever a shopping cart is no longer needed.

21. Can you explain about ajaxComplete() function?

The ajaxComplete() is called regardless of whether the request is successful or fails, and a complete callback is returned, even for synchronous queries. 

This is very useful for error handling. If a request fails but the result is not needed immediately, it is transferred to a cache, and then called later. This is especially useful if you want to keep track of failed requests and retry those that were not successful. A typical scenario is the case of an AJAX request but no data is returned, or the data is returned but not as intended. In this case, you can call ajaxComplete() to get a new set of data and continue with your business logic. A successful AJAX request is not necessarily a reason to call ajaxComplete(). you can still do other stuff while the data is being transferred from the server to the browser. For example, you can scroll, pause the video, or show a loading indicator.

22. Describe the benefits of jQuery Ajax techniques.

With the aid of DOM and JavaScript, There is a great advantage of AJAX. Ajax can request and receive data from the server without requiring a page reload. jQuery Ajax methods are a powerful way to make your web applications more responsive. They enable you to take advantage of the power of Ajax by using JavaScript to make your web pages load faster and more efficiently.

By using jQuery Ajax methods, you can take advantage of the power of Ajax by using JavaScript to make your web pages load faster and more efficiently. The following advantages of the AJAX Methods are -

23. Can you tell something about jQuery each() method?

$("img").each(function(im){    $(this).attr("width","600")});
var list = ["InterviewBit", "jQuery", "Questions"];$.each(list, function(index, value){    console.log(index + " "+ value);})
0 InterviewBit1 jQuery2 Questions
var obj = {"name":"InterviewBit","type": "jQuery"};$.each(obj, function(key,value){   console.log(key + " - " + value);})
name - InterviewBittype - jQuery

24. What is CDN?

CDN is an acronym that stands for Content Delivery Network or Content Distribution Network. It is a big distributed system of servers spread throughout the internet in many data centres. It downloads content from servers at a greater bandwidth, resulting in speedier loading times. Several firms offer free public CDNs, including Google, Amazon, Microsoft, Yahoo, etc.

25. What is the difference between javascript and jquery?

26. In jQuery, what is the difference between the $(window).load and $(document).ready functions?

$(window).load $(document).ready
$(window).load is an event that occurs when the DOM and another page's contents are fully loaded. This event occurs following the ready event. In most circumstances, the script may be run as soon as the DOM has finished loading. The ready() method is typically the ideal location to write JavaScript code

However, there may be times when you need to write scripts in the load() method. For instance, to determine the true width and height of a picture.

Once the DOM, CSS, pictures, and frames are entirely loaded, the $(window).load event is called. As a result, it is the optimal area to write jQuery code to determine the real picture size or to obtain information about anything.

When a function needs to be made available after the document has loaded, use the ready() method. Whatever code you include in the $(document).ready() method will be executed once the DOM of the page is prepared to run JavaScript code.

27. What exactly is a jQuery Data Table plug-in? Also, explain the uses with examples.

A data table plug-in is a jQuery plugin that can be used to create custom tables. It allows you to create a table with a custom layout, without having to write any code. It can be used to create tables with different layouts, or even to create tables with custom columns. The data table plug-in is a great way to add extra functionality to your websites, especially if you want to add a table to your website that is not included in the default layout.

Some of the uses for data tables are listed below -

28. What is the purpose of JQuery's serialize() method?

The serialize() method is a utility method of the jQuery library that allows you to serialize data from a DOM element and return it in a format that can be used by other libraries. 

This is useful when you want to pass data between different libraries or frameworks, or if you want to create a custom API that can be used by other developers. For example - if you want to pass JSON data from your application to a third-party API, you can use the serialize() method to serialize the data and then pass it to the API. This way, the API knows how to handle the data, and you don't have to worry about the format of the data.

The serialize() method is also useful when you need to send data between different browsers. For example - if you want to send JSON data from one browser to another, you can use the serialize() method to serialize the data and then send it using a custom HTTP request.

If you're not sure what data you need to serialize, there's an easy way to find out: Just type "serialize" into the console. You'll see a list of all the methods that are available on your element. ul> li>serialize/li> li>unserialize/li> /ul> div id="example"> ul> li>serialize/li> li>unserialize/li> /ul> /div>

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

In order to work with any element on the web page, we would first need to find it. Selectors find the HTML elements in jQuery. Some of the most commonly used and basic selectors are:

30. Explain how CSS classes can be manipulated in HTML using jQuery.

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

31. State some different types of jQuery Methods.

jQuery provides a variety of methods for doing various tasks, such as manipulating the DOM, events, and ajax. The table below covers many technique categories.

Essential Methods Characterization Classification
after(), append(), attr(), before(), etc. These methods alter DOM elements in some way, such as modifying attributes, style attributes, adding and deleting elements, and so on. DOM Manipulation
addClass(), CSS(), hasClass(), removeClass(), toggleClass(), etc. These methods retrieve and set CSS attributes of elements. CSS
attr(), html(), HTMLremoveAttr(), prop(), val(), etc. These methods retrieve and set element DOM properties. Attributes
bind(), blur(), change(), click(), focus(), keyup(), keydown(), etc. These methods deal with DOM or JavaScript events. Events
animate(), fadeIn(), fadeOut(), hide(), show(), stop(), etc. These techniques are used to provide elements of animation. Effects
get(), getJson(), post(), load(), etc. These techniques provide Ajax functionality with jQuery. AJAX

children(), closest(), each(), first(), next(), filter(),

parent(), siblings(), etc.

 These methods assist in traversing from one DOM element to another in a parent-child hierarchy, such as locating ancestors, descendants, or sister elements of a specific element. Traversing
blur(), change(), val(), submit(), etc. Forms and their many components are handled by these methods and event handlers. Forms
inArray(), isArray(), isFunction(), isNumeric(), isWindow(), isXmlDoc(), etc. Utility methods are useful for obtaining information about various objects, such as a browser, function, array, or window. Utilities

32. Explain jQuery no-conflict.

jQuery no-conflict is a jQuery option that allows you to avoid conflicts between various javascript frameworks or libraries. When you utilize jQuery's no-conflict mode, you substitute the $ variable with a new variable and assign jQuery to other JavaScript libraries. In addition, the $ symbol is utilized as a function or variable name in jQuery.

When no conflict is enabled, the $ symbol in jQuery becomes the global function name and not the library name. For example, you may use the $ function to access other libraries' data, but not their code. You can also use this option to avoid conflicts between various jQuery plugins.

33. In jQuery, distinguish between the bind(), live(), and delegate() functions.

The bind() function does not connect events to items added after loading the DOM. In contrast, the live() and delegate() methods also attach events to future items.

The distinction between live() and delegate() methods is that live() does not support chaining. It will only function on a selection or an element. However, the delegate() function supports chaining.

The bind() method works only within a dom element. If you want to bind events to items in a different element, you can use the delegate() function. The bind() method is not recommended for use in JavaScript. It is a best practice to call event handlers on items as they are added to the DOM. The bind() method is only used to control the order in which items are displayed. If you need to add items to a different order, you can use the delegate() function. The bind() method is not intended to be used in a production environment. It does not offer the same performance benefits as the delegate() method.

For Example - Consider the below code - 

$(document).ready(function(){    $("#interviewbit").find("p").live("click", function(){      alert("Welcome to InterviewBit jQuery Interview Questions");    });});

The live() method does not work in the given code, but we can easily do this using the delegate() function. So the code will be like this - 

$(document).ready(function(){    $(".interviewbit")children("p").delegate("a","click", function(){      alert("you clicked on a link to jQuery interview questions.");    });});

34. Explain the operation of the jQuery connect() method.

35. Distinguish between jquery.min.js and jquery.js.

The functionality of jquery.min.js and jquery.js is the same. However, If you are serving a page that contains a lot of JavaScript, it is a good idea to minify it. Minifying JavaScript (jquery.min.js) reduces the size of your file and makes it faster to load on all platforms. Minifying your code also reduces the chances that erroneous code will be rendered as a malicious attack because it makes it more difficult to test. With minified JavaScript, you will get better page performance, faster loading, and shorter wait times for your visitors.

There are also some of the major advantages of the jquery.min.js. - 

36. Explain the benefits of using a CDN for the jQuery files.

Hosting jQuery on a Content Delivery Network (CDN) improves availability and performance at a reduced cost and with less network traffic, improves latency (the time it takes to send and receive a data packet from the server), and provides a device-specific version of the contents.

CDNs are a great way to host your JavaScript and CSS files. By caching these files, you can reduce the amount of time it takes for your site to load, making it faster and more responsive. This is especially important for sites that serve large amounts of content, such as blogs or e-commerce sites. By using a CDN, you can also reduce the number of load times that occur when visitors access your site. In addition, by hosting your JavaScript and CSS files on a CDN, you can also reduce the amount of bandwidth that is consumed by your site.

Example - It makes it simple to maintain responsiveness for mobile screen sizes, as well as safe storage space for important data or files. 

Caching JavaScript and CSS files on a CDN is an important optimization that should be considered when building a site with a lot of JavaScript and CSS files.

37. In jQuery, what is the difference between $(this) and this.

We use this as an alternative to this.parent() to refer to the parent object in JavaScript. This is more convenient than using this.parent(). We can also use this to refer to other elements in HTML, as in an ul element:  

var myElement = $('ul').each(function() {     var childElement = this.parent().nextSibling(); });

This is useful when you need to iterate over a list of elements and their children, but you do not want to reference the parent object.

38. Can you describe the various methods for extracting a query text using regular expressions?

There are two methods for obtaining a query string using regular expressions.

39. Explain the use of event.preventDefault() method.

Event.PreventDefault is a jQuery event that stops an event from firing when the user clicks on a link or other trigger. It basically stops the default behaviour of the triggers and allows any other event to occur. It is useful for preventing unwanted events from firing when a user clicks on a link or other trigger. This can be useful when you want to prevent users from accidentally clicking on links that open up new windows or tabs.

When you use an event like click or keypress, you can prevent the event from firing by adding the event.preventDefault() method to the event object. When you use event.preventDefault(), the event will not fire unless the user clicks on a link or other trigger.

Event.preventDefault() is only available in jQuery 1.7 and later versions of jQuery.

Example - Assume you're developing an AJAX-based application in which you need to submit form data through AJAX when a button in the form is clicked. So, if you click on a button without preventing it, the button behaves normally and the website reloads. As a result, the other event will not occur when you click the button. So, if we use prevent default there, we can skip the button's default behaviour and instead perform the AJAX event and alter the HTML DOM accordingly.

40. What Are the Benefits of Using Jquery Instead of Javascript in an Asp.net Web Application?

Below are some of the benefits of using jQuery instead of javascript in ASP.net Web Application - 

41. What is event.stopPropagation()?

event.stopPropagation() stops the event from propagating up the DOM tree, preventing any parent handlers from being notified of the event. For example, if a link with a click method is linked inside of a DIV or FORM that also has a click method attached, the DIV or FORM click method will not fire.

42. Is it possible to pause or postpone the execution of the document.ready for a period of time?

Yes, that is possible. With the release of jQuery 1.6, a new method called "jQuery.holdReady(hold)" was added. This function allows you to postpone the execution of the document.ready() event. The document.ready() event is triggered as soon as your DOM is ready, however, there may be occasions when you wish to load extra JavaScript or plugins that you have referenced.

43. Would you still favor jQuery in a case when things can be done simply using javascript?

No. If we can accomplish our goals using simple JavaScript, then we should avoid using jQuery. It is because the jQuery library is always xx kilobytes in size, thus there is no use in wasting bandwidth. And because jQuery is built on top of javascript, it has numerous functions that are more complicated than the simple job you can accomplish with javascript. jQuery will also load all dependencies. It will have some speed issues as compared to the javascript code.

44. How to perform jQuery AJAX requests?

$.ajax({  url: "resourceURL",   async: false,   success: function(result){    $("div").html(result);  },    error: function(xhr){    alert("An error occured: " + xhr.status + " " + xhr.statusText);  }});

45. What does the following code do?

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

46. Write a jQuery code to create and delete cookies from the browser.

There is no direct way to access the cookies using jquery. We can easily do this with the help of pure javascript. To work with cookies in jQuery, you must install the Dough cookie plugin or any other cookies plugins. The dough is simple to use and offers a number of useful capabilities.

47. Consider the following code that exists in following HTML with the CSS:

<div id="expand"></div><style>  div#expand{    width: 50px;    height: 50px;    background-color: gray;  }</style>

Write jQuery code to animate the #expand div, expanding it from 50 * 50 pixels to 300 * 300 pixels within five seconds.

We can do this by using the animate() function. We first need to have access to the div element which has id value of expand and then apply animate function on the element as follows: 

$("#expand").animate( {   width: "300px",   height: "300px", }, 5000 );

48. Can you explain the difference between jQuery.get() and jQuery.ajax()?

49. Write a code snippet for preventing the default behavior of the submit button for performing another event.

<script>     $(document).ready(function(){         $("#submitButton").click(function(event){            event.preventDefault();         });     }); </script>

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

50. document.getElementById("interviewBit"); OR $("#interviewBit");

51. How do you disable elements in Jquery Using "attr"?

$('class_or_id_of_element_to_disable').attr('disabled', true);$('class_or_id_of_element_to_disable').attr('disabled', false);

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

We can use the following selector:

 $("[id$='IB']")

53. Explain the .promise() method in jQuery.

54. Write A Jquery Code Snippet To Sort A String Array?

$(document).ready(function(){    var arr = [ "jQuery","Interview","Questions","By","InterviewBit"];    sortedArr = arr.sort();    $("#elementId").html(sortedArr.join(""));});

The Output will be

["By","InterviewBit","Interview","jQuery","Questions"]

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

function getMinsSeconds() {  var dt = new Date();  return dt.getMinutes()+":"+dt.getSeconds();}$( "input" ).on( "click", function() {  $( "p" ).append( "Start: " + getMinsSeconds() + "<br />" );  $( "div" ).each(function( i ) {        $( this ).fadeOut( 1000 * ( i * 2 ) );  });  $( "div" ).promise().done(function() {        $( "p" ).append( "End: " + getMinsSeconds() + "<br />" );  });});

56. Can you provide an example of chaining using a code snippet?

Old Code:

$(document).ready(function(){    $('#id').addClass('ib);    $('#id').css('color', 'blue);    $('#id').fadeIn('slow');});

New Code after Chaining:

$(document).ready(function(){    $('#id').addClass('ib)    .css('color', 'blue')    .fadeIn('slow); });