Top 50 jQuery Interview Questions & Answers To Prepare in 2021

Top 50 jQuery Interview Questions & Answers To Prepare in 2021

Want to know what jQuery interview questions to expect? Here's a list of the best jQuery interview questions you might encounter during an interview.

Yash Tiwari

Published on Aug 30, 2021

16 min read

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JavaScript programmers are familiar with the name jQuery. jQuery makes it easy to write JavaScript code in a simple, elegant yet powerful way. It helps you create interactive effects, animations, and Ajax-enabled sites. Simply put, it is one of the most useful JavaScript libraries for web development. Due to its popularity, jQuery jobs are also in demand. Therefore, I have compiled a list of the 50 most-asked jQuery interview questions to help you guys ace your interview round.

You can learn jQuery to enhance your skills in JavaScript with the best jQuery tutorials.

jQuery Interview Questions & Answers For Beginners & Experts

1. What is the difference between JavaScript and jQuery?

Answer: JavaScript is an interpreted programming language. Unlike JavaScript, jQuery is a library with built-in JavaScript APIs. It is a pretty common question. Therefore, you can answer it with ease.

2. What is jQuery?

Answer: JQuery is a powerful feature-rich JavaScript library that simplifies HTML document traversal and manipulation, event handling, animation, and AJAX. jQuery has an easy-to-use API that is compatible with many browsers. Moreover, with jQuery, you can effortlessly write UI-related functions.

3. What is the difference between jQuery.get() and jQuery.ajax()?

Answer: jQuery.ajax() is the comprehensive Ajax request method offered by jQuery. It allows you to create highly customized Ajax requests, including how long to wait for a response, handle failure, if the request is blocking (synchronous) or non-blocking (asynchronous), what format to use for the response, and more.

jQuery.get() is a shortcut method that uses jQuery.ajax() internally, to create an Ajax request that is common for easy retrieval of information. Additionally, jQuery provides pre-built Ajax requests, like jQuery.getScript(), jQuery.post(), and jQuery.getJSON().

4. What are some advantages of jQuery?

Answer: jQuery offers the following advantages:

  • Clean and Simple Syntax
  • It is fast and flexible.
  • Cross-browser support.
  • It's intuitive, with open coding standards.
  • Lightweight, its core library is just 24kb.
  • It helps in event detection and handling.
  • It offers many plug-ins to cover all kinds of needs.
  • With jQuery, you can keep the code simple, clear, readable, and reusable.
  • It is like an improved version of JavaScript and does not require learning a new syntax.
  • jQuery offers extensive documentation via blogs, code snippets, tutorials, and other resources.

5. What are the effects methods used in jQuery?

Answer: We can add effects to a web page by using jQuery. jQuery effects include fading, sliding, hiding/showing, and animation effects. On a webpage, jQuery provides many methods for effects.

jQuery uses the following effects methods:

  • show() - It shows the selected elements.
  • hide() - It hides the selected or matched elements.
  • toggle() - It hides or shows the matched elements. To put it simply, it toggles between the hide() and shows () methods.
  • fadeIn() - It shows the matched elements by gradually fading them to opaque. That is, it fades into the selected elements.
  • fadeOut() - It shows the matched elements by gradually fading them to transparent. Simply put, it fades out the selected elements.

6. What is jQuery Ajax?

Answer: AJAX stands for Asynchronous JavaScript and XML. It helps us load data and exchange data with the server without refreshing the browser page. As a powerful tool for developing next-generation web applications, JQuery offers a rich set of AJAX methods.

7. What does the ajax() method do?

Answer: ajax() method sends an asynchronous HTTP request to the server.

8. What does the ajax method load() do?

Answer: The load() method loads data from a server and puts the returned data into the selected element. It is a simple, yet powerful AJAX method.

Syntax:

$(selector).load(URL,data,callback);

9. What are Events in jQuery?

Answer: The process of responding to user actions on a webpage is called events. jQuery offers basic methods for attaching event handlers to selections. Moreover, an event triggers the execution of the provided function.

10. What is the use of the CSS() method in JQuery?

Answer: CSS() method sets or returns one or more style properties for the selected element. It allows you to retrieve one or more style properties.

11. What are the categories in jquery Events?

Answer: jQuery provides methods for handling DOM events. The majority of jQuery methods complement native DOM events. Here are the following categories in jQuery events:

  • Form events
  • Keyboard events
  • Mouse events
  • Browser events
  • Document Loading

12. What is the difference between find and children methods?

Answer: Both the find and children methods are used to filter the child of the matched elements. Simply put, the find method searches all levels down the DOM tree, while the children method only searches one level down the DOM tree.

13. What’s the difference between document.ready() and window.onload()?

Answer: When a document is prepared, it fires the document.ready() event, but the window.onload() event occurs when all the content (including images) has been loaded. Typically, document.ready() is the first event fired.

14. What are the jQuery Ajax Events?

Answer: jQuery Ajax events are part of the jQuery library and are fired based on the Ajax request state.

15. What does the jQuery Ajax event method ajaxComplete() do?

Answer: ajaxComplete event is triggered by jQuery whenever an Ajax request completes. When the .ajaxComplete() method is invoked, any handlers registered with it are executed.

16. What is jQuery.noConflict?

Answer: With jQuery.noconflict, you can avoid conflicts between different Javascript frameworks and libraries. When you use jQuery.noconflict mode, you replace the $ with a new variable and assign jQuery to one or more JavaScript libraries. Additionally, $ is used for jQuery's function or variable name.

17. What are the selectors in jQuery, and what types of selectors are there?

Answer: You must first find or select an element on the web page if you wish to work with it. Selectors use jQuery to find HTML elements.

In the jQuery library, there are several types of selectors. Basic selectors include:

  • Name: This selects all elements that match the given element name.
  • #ID: It is used to select a single element that matches the given ID
  • .Class: This selects all elements that match the given Class.
  • Universal (*): It selects all elements present in a DOM.
  • Multiple Elements E, F, G: It is used to select the aggregate results of all the selected selectors E, F, or G.
  • Attribute Selector: It selects elements based on their attribute value.

18. What are the Advantages of jQuery Ajax methods?

Answer: Using jQuery Ajax methods has several advantages

  • Simple methods to use.
  • Cross-browser support.
  • The ability to load XML, HTML, JSON, or Scripts.
  • The ability to send GET and POST requests.

19. What is jQuery Mobile?

Answer: jQuery Mobile is an HTML5-based user interface system that allows responsive websites and apps attainable on smartphones, tablets, and desktop computers.

20. Is jQuery required for bootstrap?

Answer: Bootstrap uses jQuery for JavaScript plugins (including models, tooltips, etc.). However, you do not need jQuery if you only use the CSS part of Bootstrap.

21. What is jQuery connect?

Answer: jQuery connect is a plugin used to connect a function with another function. Additionally, it executes a function whenever another object or plug-in is executed.

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

Answer: The Body.Onload() event will be fired only once the DOM and associated resources like images are loaded, but jQuery's document.ready() event will be fired once the DOM is loaded, and it does not wait for the resources like images to be loaded.

23. What is the difference between the ID selector and class selector in jQuery?

Answer: Selectors for ID and class are the same as in CSS. ID selectors use IDs, whereas class selectors use a class to select elements. ID selectors let you choose a single element. However, if you wish to select a group of elements, you can use a similar CSS class to use the class selector.

24. Is it possible that jQuery HTML works for both HTML and XML documents?

Answer: No, Only HTML documents will work with jQuery HTML. It does not work for XML documents.

25. What are the key features of jQuery?

Answer: Here are the main features of jQuery:

  • Animation: This framework comes with several built-in animation effects that you can use on your website.
  • AJAX Support: jQuery lets you create a responsive and feature-rich website using AJAX technology.
  • Cross Browser Support:jQuery is cross-browser compatible and works with IE 6.0+, Safari 3.0+, Chrome, and Opera 9.0+.
  • DOM Manipulation: jQuery makes the selection of DOM elements easy, traverses them, and modifies their content by using a cross-browser open source selector engine.
  • Event Handling: It offers an intuitive way to capture multiple events, such as a user clicking a link, without cluttered HTML code with event handlers.
  • Lightweight: The size of this library is only 19KB.

26. What is the difference between jquery.min.js and jquery.js?

Answer: jquery.min.js is a compressed version of jquery.js (comments and whitespaces are removed, short variable names are used, etc.) to conserve bandwidth. Functionally, they are the same. In the production environment, it is best to use this compressed version. Moreover, your web pages will be more efficient when you use the minimized version of jQuery.

27. What is jQuery UI?

Answer: It is a set of UI interactions, effects, widgets, and themes based on the jQuery JavaScript library. Furthermore, jQuery UI is suitable for highly interactive web applications with many controls and a simple page with a date picker control.

28. Explain the difference between the .detach() and .remove() methods in jQuery.

Answer: .detach() and .remove() are the same methods, except .detach() retains all jQuery data associated with the removed elements while .remove() does not. When removed elements need to be reinserted into the DOM at a later time, .detach() is useful.

29. What is a Data Table plug-in for jQuery?

Answer: It is a plugin for the jQuery Javascript library. This tool is a highly flexible one, built upon the principles of progressive enhancement, which allows you to add advanced features to any HTML table.

30. What is the difference between prop() and attr()?

Answer: prop() and attr() are both used to get or set the value of the specific property of an element attribute, whereas attr() returns the default value of a property whilst prop() returns the current value.

31. What is Qunit?

Answer: QUnit is a robust and easy-to-use JavaScript unit testing framework. This framework is used by the jQuery, jQuery UI, and jQuery Mobile projects. Moreover, it can test any generic JavaScript code.

32. Can a jQuery library be used for server scripting?

Answer: Client-side scripting functionality is built into jQuery. However, it is not compatible with server-side scripting.

33. What is a CDN? What are the advantages of using CDN?

Answer: Content Delivery Network (CDN) is a vast distributed network of servers deployed in multiple data centers across the internet. Consequently, it provides the files from servers at a greater bandwidth that leads to a faster loading time. The following companies that provide free public CDNs are Google, Microsoft, and Yahoo.

Advantages

  • It reduces the load on the server.
  • Additionally, CDNs save bandwidth. These CDNs load the jQuery framework faster.
  • Users will see the site cached if they regularly visit any of these CDNs from a site that is using jQuery.

34. What is the difference between bind() vs live() vs delegate() methods in jQuery?

Answer:

  • bind(): By using this method, the event handler is registered directly to the DOM element. Example:
    $(“#members a”).bind(“click”, function(f){….});
    
  • live(): It attaches the event handler to the root of the document. Therefore, one handler can handle all events propagated to the root. Thus, the handler is attached only once.

  • delegate(): You can choose where to attach the handler in this method. This is the most reliable and efficient method for delegation.

    $(“#members”).delegate(“ul li a”, “click”, function(f){….});
    

35. What is the method chaining in jQuery, and what advantages does it offer?

Answer: We have written jQuery statements one after the other until now. However, Chaining in jQuery is a technique that lets us run multiple jQuery commands sequentially on the same element(s).

$("#h2").css("color","blue").animate((left: '100px'}).slideDown(1000);

Chaining only requires the button to be selected once. Whereas, without chaining, jQuery must search the entire DOM and find the button before each method is applied.

36. Differentiate among .empty() vs .remove() vs .detach() in jQuery.

Answer: Here's the difference between .empty(), .remove(), .detach() in jQuery:

  • .empty() - It does not remove the element, but removes its content along with its related child elements.
  • .remove() - It removes the element along with its child elements. Restoring DOM data is possible; however, event handlers cannot be restored.
  • .detach() - It removes both the element and its associated child elements while retaining the data and event handlers of the removed element for re-use.

37. Explain what the following code does:

$( "div" ).css( "width", "300px" ).add( "p" ).css( "background-color", "blue" );

Answer: This code uses method chaining to accomplish several things. Firstly, it selects all <divs> elements and changes their CSS width to 300px. Afterward, it adds all the <p> elements to the current selection, allowing it to change the CSS background color for both the <div> and <p> elements to blue.

38. What is the use of the toggle() method in JQuery?

Answer: When a click event occurs, toggle() attaches functions to toggle. So, on the first click, the first action occurs, on the second, the second action, and so on. For example:

<button>Change my color on each click</button>
<script>
$(document).ready(function(){
$("button").toggle(
function(){$("button").css({"color": "blue"});},
function(){$("button").css({"color": "yellow"});},
function(){$("button").css({"color": "red"});
});
});
</script>

39. What is the use of jQuery .each() function?

Answer: jQuery.each() is a general function for looping through a collection (either an object or array type). Array-like objects with a length property are iterated based on their value and index position. Other objects are iterated based on their key-value properties. However, jQuery.each() function works differently from the $(selector).each() function, which works on the DOM element using a selector. Both, however, iterate over jQuery objects.

40. Explain what the following code will do:

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

Answer: This code runs a query to retrieve any <div> element with the id first, Plus all <div> elements with the class first, further all elements which are children of the <ol id="items"> element and whose name attribute ends with the string "first". The following example shows how to use multiple selectors simultaneously. The function returns a jQuery object containing the results of the query.

41. How to perform jQuery AJAX requests?

Answer: jQuery offers the ajax() method to execute an AJAX (asynchronous HTTP) request.

Syntax:

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

Each parameter specifies a name-value pair. Here is the list of possible values:

  • url: It specifies the URL where the request will be sent. The default is the current page.

  • success(result, status,xhr): This callback function runs when the request succeeds.

  • error(xhr,status,error): The function that runs when the request fails.

  • async: Boolean value that determines whether the request should be handled asynchronously or not. The default value is true.

  • complete(xhr, status): The function that runs when the request is completed (after success and error functions have been handled).

  • xhr: The function that creates XMLHttpRequest object.

42. What is the advantage of hosting a jQuery using a CDN?

Answer: The advantages of hosting a jQuery using a CDN are:

  • This will reduce the download time for the jQuery library. Therefore, users in Europe will hit the European CDN, and users in the United States will hit the US CDN. As a result, the overall page load time will be reduced. (example)
  • If the user visited another website that uses the same jQuery library, the library will already be cached in the user's browser. In this situation, the user does not have to download the jQuery library.

43. Explain the various Ajax functions available in jQuery?

Answer: The various Ajax functions available in jQuery are:

  • ajaxStart() - You can register a handler that will be invoked when the first Ajax request begins.
  • .ajaxStop() - When all requests are completed, register the handler to be called.
  • .ajaxSuccess() - As soon as an Ajax request is completed, register the handler to be called.

44. What is the difference between width() vs css(‘width’) in jQuery?

Answer: The CSS('width') returns the width value in pixels, whereas width() returns the integer (without the unit values). For example:

div{
width: 20cm;
}

If you print the values:

$(this).width();
$(this).css(‘width’);

Accordingly, you will get values like 756 and 756 pixels. Although the width is specified in cm, it is converted to pixels (px) for output purposes.

45. Consider the following code that exists in the 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 X 50 pixels to 300 X 300 pixels within five seconds.

Answer: We can accomplish this using the animate() function. First, we need to gain access to the div element which has an id value of expanding, and then we can apply an animate function to it as follows:

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

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

Answer: The .promise() method returns a dynamically generated promise that resolves when all actions associated with the collection, queued or not, have finished. It offers two optional arguments:

  • type - The default type is “fx” which indicates that the returned promise is resolved only when all animations of the selected elements have been completed.
  • target - If a target object is specified, .promise () will attach the promise to that object and return it rather than creating a new one.

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

document.getElementById("Coursesity"); OR $("#Coursesity");

Answer:

  • The code document.getElementById( "Coursesity" ); is more efficient as its the pure JavaScript version.
  • jQuery is built on top of JavaScript and makes DOM manipulation simpler by using its methods internally. There is some performance overhead. We need to remember that jQuery is not always better than pure JavaScript, so we need to use it only if it adds value to our project.

48. Describe the use of the param() method in jQuery?

Answer: The param() method returns a serialized representation of an object or array. For example:

student = new Object();
student.name = “Mary”;
student.marks = 67;
$("div").text($.param(student);

In response to an event that invokes this code, the method will produce the following output:

name=Mary&marks=67

49. Given the following HTML:

1. <div id="expander"></div>
2. and the following CSS:
3. div#expander{
4. width: 100px;
5. height: 100px;
6. background-color: green;
7. }

Write code in jQuery to animate the #expander div, expanding it from 100 x 100 pixels to 200 x 200 pixels over the course of three seconds.

Answer:

1. $( "#expander" ).animate(
2. {
3. width: "200px",
4. height: "200px",
5. },
6. 3000 );</p>
7.

50. Explain the difference between $(this) and this in jQuery?

Answer: This is a reference to the DOM element, whereas $() is the jQuery constructor function. We use $(this) to use jQuery methods.


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