This Tutorial Lists Most Frequently Asked jQuery Interview Questions And Answers to Help You Prepare for Your Upcoming jQuery Interview:
If you are preparing for a jQuery interview, then here are the most frequently asked jQuery interview questions with answers and examples for your reference.
We have tried to bring together all the possible questions that you may likely encounter during your technical interview to check your competency on jQuery.
Let’s Explore!
Table of Contents:
What Is jQuery?
jQuery is a document object model manipulation JavaScript library, that is mainly used in managing and travel over HTML documents, web element event handling, special effects on DOM and Ajax communications and multiple browser JavaScript development.
jQuery is a lightweight JavaScript library that contains the following features:
- HTML/DOM manipulation
- CSS manipulation
- HTML event methods
- Effects and animations
- AJAX
- Utilities
List of the Top jQuery Interview Questions
Q #1) Can you explain what is jQuery?
Answer: jQuery is a fast, lightweight and feature-rich JavaScript library. It is easy to use cross-browser compatible API for HTML document traversal & manipulation, event handling, adding animation effects to web pages and helps in Ajax interactions.
Q #2) Can you differentiate between JavaScript and jQuery?
Answer: JavaScript is an open-source scripting language that makes static web pages into dynamic pages, that are used to validate form data before submitting it to a server.
jQuery is a lightweight, fast javascript library, browser compatible, used for HTML document traversal & manipulation, event handling, adding animation effects to web pages and helps in Ajax interactions.
Q #3) Explain the various jQuery effects method.
Answer: jQuery effects method help us to add some special effects to HTML elements present in DOM of web pages, and these methods can be grouped in fade, slide, hide, show and special effects.
The list of jQuery effects methods is given below.
- show(): This method can display /show the selected element.
- hide(): This method hides the element selected.
- toggle(): This method helps to toggle between show() and hide() method for the selected element.
- fadeIn(): This method helps hidden elements in the page to fade in (displayed), i.e. make hidden elements into an opaque element.
- fadeOut(): This method helps to hide an element from the web page by making the colored element transparent, in other words, it fades out.
- fadeToggle(): This method helps to modify the state of the selected element, i.e. hidden selected element into visible and visible selected element into the hidden element.
- slideUp(): This method can help selected HTML element slide upward.
- slideDown(): This method can help selected HTML element slide downward.
- slideToggle(): This method helps to modify the position of the selected element, i.e. selected element if slide upwards from its position, then it will slide down, and if the selected element slid downwards from its position, then it will slide up.
- animate(): This method can change selected elements from one state to another with CSS styles. The CSS property value such as position, color or shape changes within a particular interval resulting in an animated effect.
Q #4) Give some examples of Ajax methods in jQuery.
Answer: Ajax helps to send and retrieve data as well as change the content of the web page from a server without any need for the entire page reload. jQuery Ajax methods such as load(), get(), post() facilitate Ajax calls made by the application.
Q #5) Explain the functionality of the Ajax() method.
Answer: Ajax() method sends asynchronous HTTP requests to the server and receives the data from the server. Ajax() method is valuable as it offers the ability to specify both success and failure callbacks.
Q #6) Explain the functionality of ajax load() method.
Answer: The load() method sends HTTP requests to load data in the form of HTML or text content from a server and puts the returned data into the selected DOM element(s).
Q #7) Elaborate jQuery Ajax Events.
Answer: Ajax methods trigger an event handler that results in jQuery Ajax Events. Some of the examples of jQuery Ajax Events are as listed below.
These events are categorized into local events and global events.
- ajaxStart(): It is a Global Event, This event triggers as a result of starting of an Ajax request, provided no other Ajax request currently running.
- beforeSend(): It is a Local Event, as the name indicates, this event gets invoked before Ajax request starts, thereby allowing to modify XMLHttpRequest objects.
- ajaxSend(): It is a Global Event, and this event gets called before the Ajax request is run.
- success(): It is a Local Event. This event triggers only if the Ajax request was successfully sent ( i.e. while sending Ajax request, the event does not display any error from the server or from data).
- ajaxSuccess(): It is a Global Event, triggers only if the request sent was successful.
- error(): It is a Local Event, that gets triggered if an error occurs while executing the request. (You can have either error or a success callback while sending Ajax request)
- ajaxError(): It is a Global Event, which behaves the same as its local counterpart error() event.
- complete(): It is a Local Event. This event gets called regardless of the request being successful or result in an error, and complete callbacks are received, even for synchronous requests.
- ajaxComplete(): It is a Global Event, which behaves the same as its local counterpart complete() event, even for synchronous requests.
- ajaxStop(): It is a Global Event, that gets triggered when no Ajax requests are still being processed/ pending for processing.
Q #8) Explain the functionality of ajaxComplete() method.
Answer: The ajaxComplete() gets called regardless of the request being successful or resulting in an error, and a complete callback is received, even for synchronous requests.
Q #9) Explain the functionality of ajaxStart() method.
Answer: The ajaxStart() event is a global event that triggers as a result of the Starting of an Ajax request, provided no other Ajax requests are currently running.
Q #10) Explain some examples of Events in jQuery.
Answer: Actions on HTML elements across web pages are events in jQuery or JavaScript, thereby making dynamic web pages.
Few examples of events are listed below.
- Clicking mouse over an element such as a button.
- Sending input element values from the HTML form.
- Reset of form element to their default values or reloading a page.
- Pressing or typing any one or more than one key on the keyboard.
- Scrolling of the web page etc.
Q #11) Explain examples of some of the categories of jQuery events.
Answer: jQuery events are categorized on the basis of their types:
- Mouse Events such as click & dblclick.
- Keyboard Events such as keyup & keydown.
- Form Events such as submit, focus & change.
- Document/Window Events such as load, unload & scroll.
Q #12) Explain the functionality of the jQuery CSS() method.
Answer: CSS() method in jQuery is used to check the present value of the style property, add or change the style property of the selected element. In other words, the jQuery CSS() method is used to GET and SET the DOM element’s CSS style properties.
Q #13) Differentiate between find() and children() methods.
Answer: .find() and .children() are used to locate child of the matched DOM elements, .find() travels to any level down, whereas .children() travels a single level down to locate the element.
Let’s consider the following DOM structure in an HTML document.
Syntax in jQuery .find() API to locate element within <li> tag with class “item-ii”.
$("li.item-li").find("li").css("background-color","yellow");
The result of the above method call is a yellow background on items A, B, 1, 2, 3 and C as shown in the below image.
.find() method selects all child elements of the DOM element being traversed.
Syntax in jQuery .children() API to locate element with <ul> tag with class “level-2”.
$( "ul.level-2" ).children().css( "background-color", "yellow" );
The result of the above method call is a yellow background on items A, B, and C as shown in the image below.
.children() method selects single level elements of the DOM element being traversed.
Q #14) Explain various types of selectors and their functionality in jQuery.
Answer: jQuery selectors are used to locate/select HTML elements from the DOM hierarchy based on their attributes as listed below.
- name
- id
- class
- type
- values
Basic Selector Types are:
- Name
- ID
- Class Name
- Universal selector such as *, which selects all elements in a DOM.
- Multiple elements. Example: <li>, <p>, <span>.
- Attribute selector, Example: identify/select elements based on their attributes like color, font style or background color.
Example, of Multiple elements and Attribute selectors in jQuery, is explained below.
In the above jQuery code, the class attribute is a selector and the font color of the text inside the HTML tag element is changed to green. This code will affect/change the font color of texts inside all those elements that have class attributes.
Q #15) Differentiate between the ID and Class selector in jQuery.
Answer: Each HTML element can have only one ID, in other words, an element can be identified with a unique ID, whereas you can use the same class on multiple elements.
Example of ID selector in jQuery in order to hide a DOM element with an ID as its attribute, say <div> element with an ID as “gold_coin”
$('#gold_coin').hide();
If you want to hide, say all links having its class as “raw”,
$('a.raw').hide();
Q #16) Explain the advantages of jQuery Ajax methods.
Answer: Ajax can request and receive data from the server without page reload with the help of DOM and JavaScript.
Advantages of using Ajax methods in jQuery are listed below:
- It allows us to take out the entire page reload and gives us the flexibility to load only a part of the page.
- Simple API.
- Cross-Browser support.
- GET and POST supported.
- Upload JSON, XML, HTML or script document.
Q #17) Differentiate between onload() and document.ready() jQuery methods.
Answer: The difference between onload() and document.ready() methods is that the onload() method of JavaScript will get called only after all the objects in the web document are completely displayed/loaded.
Whereas, document.ready() method gets called when the DOM structure gets loaded in the documents. document.ready() method gets called very fast when compared to onload() method, as the later waits until the images are completely displayed.
Q #18) Explain the functionality of connect() method of jQuery.
Answer: jQuery connect() is a plugin that is used to connect/bind a function to another function by assigning a handler. We can use an event of a DOM element using this function.
Q #19) Briefly explain the bootstrap and JavaScript plug-in.
Answer: Bootstrap is a framework or toolset that includes HTML, CSS, and JavaScript to build a webpage or web application. Many of Bootstrap components require Javascript plugins to function.
Q #20) Explain the Applications for jQuery Mobile.
Answer: jQuery Mobile is an open-source cross-browser compatible framework designed to build mobile applications accessible on all smartphones, tablet and desktop devices.
jQuery Mobile is created on jQuery and User Interface of jQuery for rendering various special effects, handling Ajax request/responses, touch events, along with a variety of widgets.
Q #21) Differentiate between jquery.min.js and jquery.js
Answer: jquery.min.js and jquery.js have the same functionality, jquery.min.js has all empty spaces removed in order to make the file smaller in size and faster to load resulting in script execution.
Having JS files minified in a production environment means that they will load faster and give quick and better page performance.
Q #22) Explain the possibility of jQuery HTML method for HTML and XML document.
Answer: jQuery HTML method is not available on XML documents, it only works for HTML documents.
Q #23) Explain the functionality of jQuery UI (user interface).
Answer: jQuery UI is a jQuery library, that provides building various user interface objects such as multiple record lists where the users can select, sort, drag, drop as well as resize particular DOM elements.
UI library also creates built-in widgets such as auto-complete, checkbox, radio buttons, datepicker, menu, etc. as well as adding an effect hide, show or toggle, and other animations.
Q #24) Explain the functionality of a Data Table plug-in for jQuery.
Answer: Data Table is a jQuery plug-in that when applied to records is displayed in a tabular form.
We can sort the data across single as well as multiple columns, search the specific record, add pagination, records per page, and navigate the records in a table. Data Table can be applied to static data, Array, data in JSON as well as AJAX response.
Q #25) Explain any of the advantages of hosting a jQuery from CDN.
Answer: Hosting jQuery from the Content Delivery Network (CDN) helps in high availability and high performance at a lower cost and low network load, improved latency (lesser time is taken to send and receive a data packet from server), offer a device-specific version of contents.
Example: Responsiveness for mobile screen size, and secured storage capacity for sensitive data or files.
Q #26) Identify any difference between .detach() and .remove() of jQuery.
Answer: detach() method of jQuery removes the selected element, however it retains data and events. .remove() method of jQuery removes elements, data as well as events.
Q #27) Can I use a jQuery library for server scripting?
Answer: jQuery is a client-side scripting Javascript library. It can not be used for server-side scripting.
Q #28) Can you give some situations or scenarios for using jQuery?
Answer:
We can use jQuery in the following situations/scenarios:
- We can apply a jQuery function that can change CSS static or dynamic property.
- We can call functions on events such as Form events, Keyboard events, Mouse events, Browser events with the help of jQuery.
- We can manipulate (add, edit or delete) DOM elements using jQuery.
- jQuery can be used for animation effects on the HTML element by gradually changing its static position to another position.
Q #29) List the four parameters used for the jQuery Ajax method.
Answer: URL address where the request is sent, Type of request viz GET or POST, Data/content to be sent to the server and condition for the browser to either allow or not cache the page requested are the four parameters used for jQuery Ajax method.
Q #30) Explain the functionality of the jQuery filter.
Answer: .filter() in jQuery will check for the matched element and the attribute can be added to the matched element.
For example, for the .filter(), it can be as given below.
Line of code in jQuery.filter() API to locate/filter out list elements are as below.
$( "li" ).filter( ":even" ).css( "background-color", "yellow" );
The result of the above method call is a yellow background for texts Physics, Mathematics, History, French, etc. that is at index 0, 2, 4 and so on, (remember index starts from 0, hence 0 is an even) as shown in the image below.
Q #31) What special character is used as a shortcut for jQuery?
Answer: $ is used in the place of jQuery,
Example: jQuery(document).ready(function() ; can be used as $(document).ready(function()
Q #32) Explain the different ways in which we can debug jQuery.
Answer: There are few ways in which we can debug jQuery code.
Modern-day browsers such as Google Chrome, Mozilla Firefox, Opera and Safari have built-in Javascript debugger. To debug the jQuery code, Press F12 from your keyboard and the browser with the built-in debugger will open a UI, wherein select the ‘Console’ menu. The error will be displayed in the console menu if any.
You can write console.log() into the code to get the error text, you can also write debugger; in between the code line, due to debugger the script will start in debug mode, pressing F12 into the browser will open console which will debug the code, pressing F10 will read values of the jQuery objects, and this is how we can debug jQuery code.
Q #33) Explain the possible ways in which we can include jQuery on a page.
Answer: You can download compressed production version jquery-3.4.1.min.js from https://jquery.com/download/ site, and save it into the lib folder under the project folder.
i) We can reference jquery from the local folder at project/lib/Scripts as below.
<script src="Scripts/jquery-3.4.1.min.js"></script>
ii) We can reference from content delivery network sites such as Microsoft CDN as below.
<script src="https://ajax.aspnetcdn.com/ajax/jQuery/jquery-3.4.1.js"></script>
Q #34) Explain the functionality of .each() method in jQuery.
Answer: jQuery .each() is used to iterate / list the DOM element present in the jQuery object.
Example
var veg_list = {
Onion,
Capsicum,
Sweet Potato,
Cauliflower,
Bitter Gourd,
Brinjal
};
$.each(veg_list, function (index, value) {
console.log(value);
});
// displays output as Onion Capsicum Sweet Potato, Cauliflower Bitter Gourd Brinjal
Q #35) Differentiate between .prop() and .attr() methods of jQuery.
Answer: Following is the difference between .prop() and .attr().
Example:
jQuery code contains the attr() method that modifies attribute values of an image as shown below.
.attr() method of jQuery changes attributes like width and border of the image.
$(selector).attr(attribute of the element, value to which attributes are changed to).
.prop() method in jQuery is used to return and modify DOM properties such as checked, selected, or disabled state.
<input type="checkbox" value="pink" checked>Pink<br>
For input type as a checkbox, the value is pink and DOM property is checked,
jQuery code contains prop() method that modifies the display property of an element.
.attr() method helps us to select a value which is “pink” here, whereas .prop() method selects property which is “checked” here.
Q #36) Explain the functionality of jQuery.noConflict.
Answer: noConflict() method of jQuery is applied to resolve conflicts when we need to use frameworks, other than jQuery.
For example, many JavaScript libraries such as Mootools, prototype, zepto, etc. use $, a function or variable name, that is used as a replacement of text jQuery in the jQuery code, and in such cases, .noConflict() method allows to use $ shortcut identifier, by allowing other scripts to use it.
Q #37) Differentiate between width() vs css(‘width’) in jQuery.
Answer: There are two different methods in jQuery to change the width of an element. The first way is to use .css(property) and the other way is to use .property().
Example:
$(selector).css(property,value_change); $(selector).property(value_change);
In .css(property) which in this case is width, we have to add px in the value_change, say 300px.
We can use .property(value_change), which in this case is width, and you need not have to add px, but direct value.
Q #38) Where can we apply the param() method in jQuery?
Answer: We can display array, plain object or jquery object in the form of a stream of bytes so that they can be stored into memory, file or database using param() method in jQuery.
Q #39) Differentiate between $(this) and this in jQuery.
Answer: $(this) is a jQuery object, whereas this is a JavaScript’s global object reference, using this we can refer DOM element in HTML document.
$(this) references to the parent object, whereas this refers to a DOM element, which in the case of an array, represents an object with .each() method, that displays the current iteration.
Q #40) Describe the functionality of read cookies, write cookies and delete cookies in jQuery.
Answer: When websites are visited, cookies are data values such as the name of the user that gets stored in small text files on the computer. While revisiting websites, the cookies help to remember the user’s name. JavaScript and jQuery create, read and delete cookies, with the document.cookie property.
Q #41) What is the use of the serialize() method in jQuery?
Answer: It serializes the form values so that its serialized values can be used in the URL query string while making an AJAX request.
.serialize() method of jQuery returns the input values of HTML form in the form of string.
Q #42) What is the use of the val() method in jQuery?
Answer: .val() method helps to find the value of an attribute of HTML element. For example, form elements such as input, select and textarea. Val() is also applied to find the value of all matched elements from checkboxes and radio buttons as well as a drop-down list.
Example explained with syntax
// form elements such as dropdown with select tag and id mylst, the value of the selected option will have syntax as below $( "select#mylst option:checked" ).val(); // form element such as a set of radio buttons with input type as radio and name rdobtn, the value can be retrieved $( "input[type=radio][name=rdobtn]:checked" ).val();
Q #43) What is Method Chaining in jQuery? What advantages does it offer?
Answer: With jQuery method chaining, multiple actions can be applied on a single line of code, as all the methods return jQuery objects that can be utilized to call another method.
Without chaining, jQuery methods are called one after another in a separate line, whereas with chaining, jQuery methods are written in dot separated single line of code.
Without chaining multiple lines of code that need to be written, making jQuery to search entire DOM for matched element, then single methods in each line of code are applied. Whereas Chaining needs only a one-time selection of a matched element from DOM, by making better performance.
Q #44) What is the difference between jQuery.get() and jQuery.ajax() ?
Answer: jQuery.ajax() method is used to send HTTP Ajax requests, whereas jQuery.get() method is used to send HTTP GET requests to load data from the server.
Q #45) What is QUnit?
Answer: QUnit is a framework, which tests JavaScript code written for jQuery, jQuery UI, and jQuery Mobile, uses assertions and test fixtures for verifying the expected results.
Q #46) How jQuery stores data related to an element?
Answer: jQuery.data() method aids in attaching any type of data to DOM elements, free from memory leaks. jQuery makes sure that data is removed along with the DOM elements removed via jQuery methods.
Code for Storing and retrieving data related to an element.
$('#myDiv').data('keyName', { foo : 'bar'});
$('#myDiv').data('keyName'); // { foo : 'bar'}
Q #47) Can you explain the various procedures of extracting a query string with regular expressions?
Answer: We can accomplish extracting a query string with regular expression in the following two ways.
- String-based approach: This method helps in deriving String by comparing equivalent regular expression, using .replace() method.
- Regular expression approach: A most powerful method for extracting a query string and pattern must be used that is compared with strings in JavaScript. Using .exec() and .test() methods for comparing with patterns. match(), matchAll(), replace(), search() and split() are other few methods for String.
Q #48) Explain the concept of the finish method in jQuery.
Answer: In order to stop all the queued animations and to help them place in their final state the .finish() method is used.
Q #49) Differentiate between calling stop (true, true) and finish method.
Answer: .finish() method helps in clearing the queue & helps the animations to enter into their end state, whereas .stop() method is called on an element, by forcing currently running animation to stop instantly.
Q #50) How can you write a browser-specific code using jQuery?
Answer: We can write browser-specific code in jQuery using navigator.userAgent to identify, the browser from Internet Explorer, Chrome, Firefox, Safari, and Opera, as the code written below.
if (navigator.userAgent.search("MSIE") >= 0) {
// JQuery Code once navigator.userAgent identifies Microsoft Internet Explorer browser.
}
else if (navigator.userAgent.search("Chrome") >= 0) {
// JQuery Code once navigator.userAgent identifies Google Chrome browser.
}
else if (navigator.userAgent.search("Firefox") >= 0) {
// JQuery Code once navigator.userAgent identifies Mozilla Firefox browser.
}
else if (navigator.userAgent.search("Safari") >= 0 && navigator.userAgent.search("Chrome") < 0) {
// JQuery Code once navigator.userAgent identifies either Safari or Chrome browser type.
}
else if (navigator.userAgent.search("Opera") >= 0) {
// JQuery Code once navigator.userAgent identifies Opera browser.
}
Q #51) What is the procedure to check the data type of any variable in jQuery?
Answer: jQuery function type() is used in order to identify the data type of any variable such as an array, string, number, function or object data type.
Conclusion
jQuery is a document object model manipulation JavaScript library, mainly used in HTML document traversing and Cross-browser JavaScript development that creates DOM and Ajax animations to manage browser events.
Hope you found the answers to the most frequently asked interview questions on ‘jQuery’ to be of immense help. Practice as many questions as possible and be confident.
Further reading =>> Popular AJAX Interview Questions and Answers
All the best for your interview !!