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jQuery - Interview Question

Crack your next job interview easily with these most asked jQuery interview questions and answers for both freshers and experienced professionals. jQuery, the commonly used JavaScript library, is used by numerous websites across different industries.

If you are appearing for a web developer job in any field, you must go through these common interview questions on jQuery. It will help you stay prepared and boost the chances of selection. 

You would also love to go through our complete jQuery tutorial to learn all the concepts with notes, videos, quizzes, and more.

Interview Questions

jQuery is a client-side JavaScript library that is fast, lightweight, and feature-rich. It is a free JS library that makes interacting with HTML/CSS documents easier, specifically the Document Object Model (DOM) and JavaScript.

jQuery simplifies HTML document traversal and manipulation, browser event handling, DOM animations, AJAX interactions, and cross-browser JavaScript development, just to name a few things.

Here is a quick list of jQuery benefits:

  • The most widely used and open source JS library

  • Very quick and easy to customize and extend

  • Allows creation of cross-browser-compatible web applications because it works similarly across all browsers

  • Improves the performance of an application as it compresses the original JS file. The web page loads and works faster when the file size is reduced.

  • UI-related functionalities are frequently implemented with few lines of code.

jQuery is a JavaScript library that includes DOM/CSS manipulations, event effects or animations, AJAX functions, and various commonly used plugins.

No. Only HTML documents are supported by jQuery.

The following are some of jQuery's key features:

  • The Sizzle engine allows for simple DOM manipulation

  • AJAX support and event handling

  • Effects and animations are already included

  • It's a small library

  • Compatibility across browsers

  • CSS3, basic XPath, and HTML5 are supported

The css() method changes the selected element's style property.

The jQuery length property is used for counting how many elements are there in an object.

When we click on an HTML element, the jQuery click event occurs. The click() method in jQuery helps trigger the click event.

When a paragraph tag element is clicked on a browser page, click() will fire the click event.

The following are some of the methods that produce the desired effect:\

  • jQuery toggle() Method

  • jQuery slideDown() Method

  • jQuery Effect fadeOut() Method

  • jQuery fadeToggle() Method

In jQuery, the each() method allows us to loop through various datasets such as arrays or objects (even DOM objects).

It can iterate over a collection of DOM objects using the same selectors.

For example, if you want to add width="700" to all of the images on a page, you can select all of the pictures and loop through them, adding width="700" to each tag. The code can be written as follows:

$("img").each(function(im){

    $(this).attr("width","700")

});

$ is a jQuery object definer. "this" is a DOM object in the above syntax, and we can only apply jQuery functions to jQuery objects, so we wrap it in the $ definer to convert it to a jQuery object.

  • Each() can also iterate over data arrays, returning the index and value of each data position.

For Example:

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

Output:

0 Tutorials Freak

1 jQuery

2 Interview Questions

You can also loop through objects with each().

For Example:

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

The above code prints:

name - Interview Questions

type - jQuery

JavaScript is a C-based interpreted language that combines ECMAScript and the Document Object Model (DOM). Whereas, jQuery is a JavaScript library designed to speed up and simplify JavaScript. 

ECMAScript is not supported by jQuery. In contrast to JavaScript, which requires long lines of code to code a functionality, jQuery imports the library and calls the functions, reducing the programmer's coding effort.

Because JavaScript does not support cross-browser compatibility, a developer must implement the functionality manually. In contrast, jQuery has built-in cross-browser code compatibility.

These are some of the primary differences between JavaScript and jQuery.

We must first locate any element on the web page before working with it. In jQuery, selectors are used to find HTML elements. 

Some of the most common jQuery selectors are listed below:

  • Name: This is used to select all features similar to the given element. Name.

  • #ID: This selector is used to find a single piece that matches the given ID.

  • Class: This is used to select all elements with the same class.

  • The universal (*) selector selects all elements in a DOM.

  • Multiple Components E, F, and G: These selectors combine the results of all the specified selectors E, F, and G.

  • Attribute Selector: This selector chooses elements based on their attribute values.

jQuery has a number of methods for manipulating the CSS classes that have been assigned to HTML elements. AddClass(), removeClass(), and toggleClass() are the most important methods ().

  • addClass()

This method applies one or more classes to the elements that have been selected.

Syntax

$(selector).addClass(className);

You can also call to add multiple classes to the selector addClass(className). 

Syntax:

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

  • removeClass()

This method works similarly to addClass(). It removes classes from elements.

With the removeClass() method, you can remove a single class, multiple classes, or all classes from the selected elements.

Syntax:

  • For removing one class: 

$(selector).removeClass(class1);

  • For removing multiple classes: 

$(selector).removeClass(class1, class2, class 3);

  • For removing all classes at once: 

$(selector). removeClass()

  • toggleClass()

This method is used to add or remove one or more classes from the selected elements, with the class being removed if the selected element already has it. 

It adds the specified class if it doesn't already exist; otherwise, it toggles the class application.

Syntax

$ (selector).

toggleClass(className);

Using the Dough cookie plugin, we can deal with cookies in jquery. The dough is simple to use and packs a punch.

Create cookie in jQuery:

$.dough(“cookie_name”, “cookie_value”);

Read Cookie in jQuery:

$.dough(“cookie_name”);

Delete cookie in jQuery:

$.dough(“cookie_name”, “remove”);

The children() method is used to find all the children elements related to the selected element, while the find() method is used to find all the descendant elements of the selected element.

The ‘this’ keyword is used in a conventional manner to refer to DOM elements in JavaScript. Whereas, if we put the ‘this’ in $(), it becomes a jQuery object.

Both are used for the same purpose, which is to refer to DOM elements. However, ‘this’ can be used for calling all the DOM methods, but not jQuery methods. On the other hand, $(this) can be used for calling jQuery methods and functions. But you can’t use it for DOM methods.

The $.ui.version command returns the jQuery UI version.

jQuery connect is a plugin that allows you to link or bind one function to another. It is used to execute a function or plugin from another function or plugin.

  • From jQuery.com, get the jQuery connect file.

  • Incorporate that file into the HTML document.

  • To connect one function to another, use the $.connect function.

The param() method in jQuery is used to create a serialized representation of an object.

css() method in jQuery is used to change the selected element's style property. This property can be used in a variety of ways.

The jQuery.size() method returns the number of elements matched by the given selector. On the other hand, jQuery.length returns the number of elements in the jQuery object. Because it avoids the overhead of a function call, the jQuery.length property is preferred.

Because jQuery supports.net applications, we can call C# code from it.

The ID selector selects elements by ID, whereas the class selector selects elements by class. 

Therefore, only one element can be chosen with an ID selector. However, the class selector can determine a group of elements that all have the same CSS class.

The data|info|information} is associated with the DOM nodes and objects using jQuery.data method. This data method simplifies and condenses the jQuery code.

For JavaScript plugins, Bootstrap uses jQuery (like models, tooltips, etc.). However, you don't need jQuery if only the CSS part of Bootstrap is used.

There are three types of selectors in jQuery:

  1. XPath Selector 

  2. CSS Selector

  3. Custom Selector

The functionality for client-side scripting is built into jQuery. Unfortunately, server-side scripting is incompatible with jQuery.

QUnit is a flexible unit testing framework for JavaScript. It can test any generic JavaScript code and is used by the jQuery, jQuery UI, and jQuery Mobile projects.

To reference a jQuery and save it in a variable, use the 'NoConflict' method. Then, instead of Sign, use that variable.

You can disable jQuery animation by setting the jQuery property "jQuery.fx.off" to true.

  • attr(): It obtains the attribute value for the first element in the set of matched elements.

  • prop(): It returns the value of the first element in the set of matched elements' properties. It first appeared in jQuery 1.6.

The $(window).load event triggers when the DOM and other page contents are fully loaded. After the ready event, this event is fired.

The script can usually be run as soon as the DOM has fully loaded. JavaScript code is usually best written in the ready() method. However, you may need to use the load() function to write scripts on occasion. 

To retrieve the real width and height of an image, for example. Once the DOM, CSS, images, and frames are fully loaded, the $(window).load event is triggered.

It's a client-side scripting library.

No, jQuery is not a W3C standard.

The ready() function is where the jQuery code begins. When the DOM is loaded, it is run.

AJAX stands for Asynchronous JavaScript and XML. It is a technology that allows the loading of pages and exchange of data with the server without refreshing it on the browser. JQuery is a fantastic tool for developing next-generation web applications because it includes many AJAX methods.

The server receives an asynchronous HTTP request from this method.

The load() method makes an HTTP request to the server to fetch HTML or text content and add it to the DOM element (s).

When preparing to send an Ajax request, jQuery checks to see if any other Ajax requests are pending. If none are currently active, jQuery triggers the ajaxStart event. At this point, any handlers registered with the.ajaxStart() method are executed.

The class and id selectors in jQuery work similar to that of CSS. The dot (.) followed by the class name is used for choosing elements by class, whereas, the hash (#) followed by the ID name is used for choosing elements by ID.

The advantages of using jQuery Ajax methods are as follows:

  • Cross-browser compatibility

  • Simple techniques to employ

  • Sending GET and POST requests is possible.

  • JSON, XML, HTML, and Scripts can all be loaded.

jquery.min.js is used for saving bandwidth as it compresses the jquery.js, which includes compression of whitespace, comments, variable names, etc.

jQuery Mobile is an HTML5-based user interface system that makes responsive websites and apps available on smartphones, tablets, and desktop computers.

No. jQuery HTML is only compatible with HTML documents. For XML documents, it does not work.

jQuery UI is a user interface interaction, effects, widgets, and themes based on the jQuery JavaScript Library. It is suitable for building highly interactive web applications with a large number of controls and a simple page.

jQuery Data Table is a plugin offered by the JavaScript library to improve the tables in HTML. It is a great plugin for showing the data in tables in a better and more user-friendly manner. 

The DataTable in jQuery is flexible that also makes accessibility of data in HTML tables easier. Furthermore, you can use it for developing dynamic data tables, with options to add pagination, sorting, ordering, and a number of more features.