jQuery Interview Questions

by Pooja Chikara

0 3204

Everyone gets apprehensive getting ready for an interview and it's entirely expected to re-examine everything and being arranged in advance. To deal with your anxiety and get you ready for a meeting, we have thought of the most posed and significant inquiries that you will experience in any interview in regards to jQuery.

Demonstrating your value before an Interviewer is of most extreme significance in the present testing and merciless rivalry world. Thus, get ready and gain from the best. These inquiries are curated by our specialists to deal with any fresher or experienced applicants.

Top 43 jQuery Interview Questions

1 What is jQuery?

jQuery is a javascript library that is created to make the common tasks trivial because using raw JavaScript can result in dozens of lines of code for each task.

2 What are the advantages of jQuery?

jQuery is small, lightweight, and easy to learn for beginners
The motive behind the creation of jQuery is: Write less, do more
It is a platform-independent technology
Cross-Browser Support
Support latest technologies
Retrieve information from a server without refreshing a page
Simplify common JavaScript tasks

3 Does jQuery work for both HTML and XML documents?

No, jQuery can work only for HTML documents.

4 What are the jQuery functions used to provide effects?

jQuery provides a range of methods that are used to add effects on a web page HTML elements in less efforts.

Display effects:

1. hide()

2. show()

3. toggle()

Fading effects:

1. fadeIn()

2. fadeout()

3. fadeToggle()

4. fadeTo()

Sliding effects:

1. slideDown()

2. slideUp()

3. slideToggle()

Additional effects:

1. animate()

2. delay()

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

css() jQuery method is used to fetch and set the style properties of the selected HTML element. This method can return the required style property value of the first matched HTML element from the selected elements.

This method can also set the CSS properties of all matched elements at a single glance.

Syntax:

This method has four different signatures which used to work for different tasks:

$(selector).css("property") ;

This syntax is used to get the CSS property value of the selected element.

$(selector).css("property","value");

The given syntax of css() method is used to set the value of the CSS property of the selected HTML element.

For more details click here

6 Is jQuery a programming language?

jQuery is not a programming language it’s a javascript library that is used to make tasks easier.

7 What is the difference between JavaScript and jQuery?

8 Is jQuery replacement of JavaScript?

No, jQuery is not a replacement for javascript we can use both in a single document at a time.

9 What is $() in the jQuery library?

The $() function (jQuery() function) returns a special JavaScript object containing an array of the DOM elements that match the selector. This object possesses a large number of useful predefined methods that can act on the group of elements.

Syntax:

$(document).ready(function(){
  // jQuery code
});

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

This jQuery method is used to perform the toggle event between hide and show effect on the selected HTML element. On the other hand, we can say that this method hides the showing of the element and show the hidden element.

Syntax:

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

Parameter description:

speed: This parameter is used to set the speed of showing and hiding. It can be "slow", "fast" or any time in milliseconds. It is optional.
callback: This represents a function that is executed after the completion of the toggle() method. It is also optional.

For more details click here!

11 What is the purpose of fadeToggle() method in JQuery?

This jQuery method is used to perform a toggle between fade in and fade out to the selected HTML elements.

Syntax:

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

Parameter description:

speed: This parameter is used to set the speed of fading in and out. It can be "slow", "fast" or any time in milliseconds. It is optional.
callback: This represents a function which to be executed after the completion of fadeToggle() method. It is also optional.

For more details click here!

12 What is the use of delay() method in JQuery?

This jQuery method is used to delay the execution of a range of queued functions on a selected HTML element.

Syntax:

$(selector).delay(speed,functionName);

Parameter description:

speed: This parameter used to set the duration of the effect. It can be "slow", "fast" or any time in milliseconds. It is optional.
functionName: This represents a function to be executed. It is also optional.

13 What are jQuery Selectors?

jQuery selectors are used to finding or querying HTML elements on the basis of their attributes. On the basis of their usability, these are one of the most important parts of the jQuery library.

jQuery supports most of the CSS selectors like element selectors, ID selectors, class selectors, etc.

There are mainly three types of selectors used in jQuery.

Element selector
ID selector
Class selector

Element selector: This selector is used to select HTML elements based on the element name.

Syntax:

$("elemnt_name")

Where element_name represents the name of element or elements which we want to select to perform an action.

#ID selector: This selector is used to find or select a specific HTML element by using their ID attribute.

Syntax:

$("#id_name")

Where id_name represents the id of the element which we want to select to perform an action.

For example:

$("#id1"), selects the element which has the id name id1.

.Class selector: This selector is used to select the HTML elements on the basis of their class attribute.

Syntax:

$(".class_name")

Where class_name represents the class of the element or elements that we want to select to perform an action.

For example:

$(".class1 "), selects the element which has the class name class1.

For more details click here!

14 Difference between .empty(), .remove() and, .detach() in jQuery?

empty(): This jQuery method is used to remove all content inside the selected element including all child elements and their content but the selected element does not removed by this method.
remove(): This jQuery method is used to remove the selected HTML element from the page. It removes all content inside the selected element including all child elements and their content. It also removes all event handlers attached to the selected element and their child elements.
detach(): This jQuery method is used to remove the selected element with its child elements and event handlers from the web page. This method prepares a copy of the removed elements to reinsert them on the web page.

15 Mention the compatible operating systems with jQuery

Mac
Windows
Linux

16 What is the use of html() method in JQuery?

This jQuery method is used to fetch and set the content of the selected HTML element.

Syntax:

This method has three different signatures which used to work for different tasks:

$(selector).html() ;

This syntax is used to get the HTML content of the selected element. It has no parameter.

$(selector).html(content);

The given syntax of html() method is used to set the content of the selected HTML element.

Parameter description:

content: This parameter represents the new content to be set to the given selected element. It is mandatory.

$(selector).html(function(index,currentcontent));

This method is also used to set the content of the selected element by using a user-defined function.

For more details click here!

17 Is jQuery library used for server scripting or client scripting?

It is a library for client-side Scripting.

18 What is the initial unit of code execution in jQuery?

$(document).ready() function is the starting point of jQuery code.

19 Define slideToggle() effect?

This jQuery method is used to toggles slideUp() and slideDown() methods to the selected HTML elements.

Syntax:

$(selector).slideToggle(speed,callback);

Parameter Description:

speed: This parameter is used to set the duration of the effect. It can be "slow", "fast" or any time in milliseconds. It is optional.
callback: This represents a function which to be executed after the completion of the slideToggle() method. It is optional.

For more details click here!

20 What are events in jQuery?

To make a page dynamic and responsive, we need to perform some actions on the HTML DOM elements. These actions are called events.

Some most useful HTML DOM events are listed below:

Mouse events:

1. click

2. dblclick

3. mouseenter

4. mouseleave

keyboard events:

1. keyup

2. keydown

3. keypress

form events:

1. submit

2. change

3. blur

4. focus

Document/Window Events:

1. load

2. unload

3. scroll

4. resize

For more details click here!

21 What is the use of jQuery.length?

This property is used to count the number of elements in a jQuery object.

22 What is jQuery click event?

When a user clicks on the HTML element, the click() function is executed which attaches an event handler method to that particular HTML element.

Syntax:

$(selector).click(function(){
//actions go here
    });

Where selector represents a jQuery selector that is used to select the HTML element on which the events occur.

For more details click here!

23 What do you understand by each() jQuery method?

This jQuery method is used to perform a specific task on every matched HTML element with the help of a function.

In a special case to stop this method on several points before applying the function on every matched element, we can return FALSE by the function and stop the loop early.

Syntax:

$(selector).each(function(index,element));

Parameter description:

function(index,element): This parameter represents a function to run for every matched HTML element. It is mandatory and has some additional parameters:

1 index: This parameter represents the index position of the selector.

2 element: This parameter represents the current element. We can also use this selector for self-referencing.

24 Explain jQuery CSS classes.

jQuery addClass(): This jQuery method is used to attach one or more class to the selected HTML elements. This method only adds the given class to the element without removing the existing classes.

Syntax:

$(selector).addClass(class_name,function(index,currentclass));

Parameter description:

class_name: This parameter represents the name of class or classes to be attached to the selected element. It is mandatory.
function(index, currentclass): This represents a user-defined function that returns the names of one or more classes to attach to the selected HTML element.
index: This parameter is used to get the index position of the element in the set.
currentclass: This parameter is used to return the current class name of the selected element.

jQuery hasClass(): This jQuery method is used to check whether a class is attached to any of the selected HTML elements or not. The return type of this method is Boolean means this method returns TRUE if any of the selected HTML element have the given class otherwise returns FALSE.

Syntax:

$(selector).hasClass(class_name);

Parameter description:

class_name: This parameter represents the name of class or classes to be check to attach to any of the selected elements. It is mandatory.

25 What is the use of serialize() method in JQuery?

This jQuery method is used to build a URL encoded text string or query string by serializing the values of the given form elements. It provides the selection facility between all form elements means we can select one or more form elements to serialize.

The serialized string creates by this method can be used as a URL query string during an AJAX request.

Syntax:

$(selector).serialize();

This method has no parameter

26 What is the use of val() method in JQuery?

This jQuery method is used to fetch and set the value of the selected HTML element means this method returns the value of the first matched HTML element from the selected elements.

It can also set the value of all matched elements. Most of the time this method is used to set or return the value of HTML form elements.

Syntax:

This method has three different signatures which used to work for different tasks:

$(selector).val() ;

This syntax is used to get the value of the selected element. It has no parameter.

$(selector).val(value);

The given syntax of val() method is used to set the value attribute of the selected HTML element.

Parameter description:

value: This parameter represents the new value to be set as the value attribute of the given selected element.

$(selector).val(function(index,currentvalue));

This method is also used to set the value attribute of the selected element by using a user-defined function.

Parameter description:

function(index,currentvalue): This represents a user-defined function which return the new value to set as value attribute of the selected HTML element. It is optional.
index: This parameter is used to get the index position of the element in the set.
currentcontent: This parameter is used to return the current value attribute of the selected element.

For more details click here!

27 What is $.noConflict?

This jQuery method is used to stop the confliction from the uses of $ symbol by different jquery frameworks. This method let out the control of $ variable from the jQuery library so that other custom library can use it without any disturbance in any functionality.

Syntax:

$.noConflict(removeAll);

Parameter description:

removeAll: This parameter is used to set the jquery’s control over all variables including 'jQuery' will be released or not. It is an optional Boolean parameter.

28 What is the difference between prop and attr?

prop(): This jQuery method is used to fetch and set the property value of the selected HTML elements. It returns the specific DOM property value of the first matched HTML element from the selected elements. On the other hand, it set the value of the specific DOM property of all selected elements.

attr(): This jQuery method is used to fetch and set the attributes and their values of the selected HTML elements. It returns the specific attribute value of the first matched HTML element from the selected elements. On the other hand, it set the value of the specific attribute of all selected elements.

prop() and attr() both jQuery methods are used to get and set the attribute values. The main difference between the working of these methods is prop() method is work on DOM properties like tagName, nodeName, and default checked or user define custom properties. On the other hand, attr() method works on HTML attributes.

29 Define slideToggle() effect?

This jQuery method is used to toggles slideUp() and slideDown() methods to the selected HTML elements.

Syntax:

$(selector).slideToggle(speed,callback);

Parameter description:

speed: This parameter is used to set the duration of the effect. It can be "slow", "fast" or any time in milliseconds. It is optional.
callback: This represents a function which to be executed after the completion of the slideToggle() method. It is optional.

For more details click here!

30 What is the use of jQuery.ajax method()?

This jQuery method is used to carry out AJAX (asynchronous HTTP) requests. It is a legitimate but most used and secure jQuery ajax method. All the ajax methods used in jQuery need the ajax() method to fulfill their work internally. When the other jQuery ajax methods are unable to perform any task, then ajax() method is used.

Syntax:

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

Parameter description:

The parameters represent one or more name/value pairs for the AJAX request. All possible pairs for this parameter are:

type: Specifies the type of request (GET or POST).
url: Specifies the URL to send the request to. The default is the current page.
contentType: The content-type used when sending data to the server. The default is "application/x-www-form-urlencoded".
dataType: The data type expected of the server response.
data: Specifies data to be sent to the server.
success(result,status,xhr): A function to run when the request succeeds.
error(xhr,status,error): A function to run if the request fails.

31 What is the jQuery Unbind() method?

This function is used in jQuery to remove one or more event handlers to one or more HTML DOM elements. It stops a function to run when the event occurs.

This function can also unbind event handlers using an event object.

Syntax:

$(selector).unbind(event,function,eventObj);

Parameter description:

event: This parameter represents one or more events to remove from the elements. Multiple event values can be added by separating each of them by commas. It is an optional parameter.
function: This represents a function that you want to unbind from the specified event for the element. It is also an optional parameter.
eventObj: This represents the event object to remove to use. It is also an optional parameter.

For more details click here!

32 Define $.animate() method?

This jQuery method is used to the custom animations efficiently.

Syntax:

$(selector).animate({params},speed,callback);

Parameter description:

params: This parameter is used to specify the CSS properties that are to animate the selected HTML elements. It is required.
speed: This parameter is used to set the duration of the effect. It can be "slow", "fast" or any time in milliseconds. It is optional.
callback: This represents a function which to be executed after the completion of the animate() method. It is optional.

For more details click here

33 What is the difference between the bind() and live() method in jQuery?

bind(): This function is used In jQuery to attach one or more event handlers to one or more HTML DOM elements. It binds a function to run when the event occurs. The working of this function is the same as the working of jQuery on() method.

Example:

<html>
 <head>
 <title>jQuery Example</title>
 <script type = "text/javascript"
        src="https://ajax.googleapis.com/ajax/libs/jquery/3.5.1/jquery.min.js">
      </script>
<script>
$(document).ready(function(){
  $(".bt").dblclick(function(){
  $(this).css("background","green");
    $("body").css("background","yellow");
  });

   $("p").dblclick(function(){
    $(this).css("display","none");
  });
});
</script>
 </head>
 <body>

<h2>jQuery Bind event Example</h2>

<p>Double click on me to hide me.</p>
<p>Double click on me to hide me.</p>
<button class="bt">Double Click me to change the color of background</button>

 </body>
</html>

live(): The Live method can bind event handlers for currently existing items or future items.

34 What $(document).ready(function()) is and when to use it?

jQuery provides a simple way to trigger the execution of code once the HTML DOM tree has loaded means the jQuery code runs after the document is finished loading or ready.

Syntax:

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

});

We can also use the below shorter syntax:

$(function(){

  // jQuery code write here...

});

35 What is the starting point of code execution in jQuery?

$(document).ready() function is the starting point of jQuery code. It is executed when DOM is loaded.

36 What is the difference between find and children methods?

find(): This jquery method is used to fetch all descendent elements of the selected HTML elements. If we talk about the DOM traversal tree, this method traverses all descendent or children of the DOM tree.

Syntax:

This method has two different signatures.

$(selector).find(filter) ;

Parameter description:

filter: This parameter is used to represents to narrow down the ancestor search. It can be an expression, element, or jQuery object. It is optional.

$(selector).children(filter);

Parameter description:

filter: This parameter is used to filter the search for descendent. It can be an expression, element, or jQuery object. It is required.

children(): This jQuery method is used to fetch all direct children of the selected HTML elements. If we talk about the DOM traversal tree, this method traverses the one level downward of the DOM tree.

Syntax:

$(selector).children(filter);

Parameter description:

filter: This parameter is used to represents a selector expression to narrow down the search for children. It is optional.

37 What is a CDN?

CDN stands for Content Delivery Network or Content Distribution Network. Following companies provide free public CDNs:

Google
Microsoft
Yahoo

38 What are the features of jQuery?

HTML manipulation
DOM manipulation
DOM element selection
CSS manipulation
Effects and Animations
Utilities
AJAX
Cross-Browser Support
Lightweight
Support latest technologies

39 What does the ajax method load() do?

This jQuery function is worked when the load event occurs or it binds an event handler with the element when a load event occurs.

A load event happens when a specific HTML DOM element is loaded to the page.

This method mainly works for the elements which contain URL property for example: image, script, frame, iframe, and window objects.

If the image is cached, the load event does not occur, which is the major problem with some browsers like Firefox and Internet Explorer.

40 What is the delegate() method in jQuery?

The delegate() jQuery function binds one or more event handlers with the specific HTML elements that are children of selected HTML elements.

This method provides a function to run when the events occur.

If we create an element in runtime by script, this method will also work for that element.

Syntax:

$(selector). delegate(child_selector,event,data,function);

Parameter description:

child_selector: This parameter represents one or more child elements to attach to the event handler. It is a mandatory parameter.
event: This parameter represents one or more events to attach to the elements. It is also mandatory.
data: This represents the additional data to pass to the function. It is an optional parameter.
function: It represents the function to run when the event occurs.

For more details click here!

41 Describe the use of the param() method in jQuery?

This jQuery method is used to create a serialized representation of an array or an object given by the user. Or we can say that this method produced a query string by using the key and values of an array or an object.

Syntax:

$.param(object,trad);

Parameter description:

object: This parameter represents an array or an object which you want to serialize by this method. It is a mandatory parameter.
trad: This parameter is used to determine whether or not to use the traditional style of param serialization. It is an optional Boolean parameter.

42 What is the use of append() method in JQuery?

This jQuery method is used to insert the given content at the end of the selected HTML element means this method inserts the specified content as the child element by the user at the end of the matched element.

Syntax:

$(selector).append(content,function(index,html));

Parameter description:

content: This represents the contents to be inserted at the end of the selected element. It can be either plain text or it may contain HTML tags. It is a mandatory parameter. Possible values for this parameter are:

HTML elements

DOM elements

jQuery objects

function(index,html): This represents a function used to return the content to insert. It is optional.
index: This parameter is used to get the current HTML of the selected element.

For more details click here!

43 What do mean by jQuery traversing?

In jQuery, traversing is used to select an HTML element or elements based on their relation to other HTML elements.

The traversing process contains a number of steps that starts by one selection and go ahead until you traversed the required element.

There are few terms which used in traversing in jQuery:

Ancestor: It represents the parent, grandparent, great-grandparent, and other such types of elements that have parental relation to the selected element.
Descendant: It represents the child, grandchild, great-grandchild, and other such types of elements that are children of the selected elements in relation.
Sibling: Siblings are the elements that have the same parents as the selected element.