Top 50+ jQuery Interview Questions and Answers – 2025

jQuery, a fast and lightweight JavaScript library, has been a game-changer in simplifying front-end web development known for its simplicity, ease of use, and cross-browser compatibility.

In this article, we will provide the Top 50+ jQuery Interview Questions 2025 tailored for both freshers and experienced professionals. Here, we cover everything, including core jQuery concepts, DOM manipulation, event handling, AJAX, animations, plugin development, and more, that will surely help you to crack jQuery interviews.

Basic jQuery Interview Questions

1. What is jQuery?

jQuery is a lightweight “write less, do more” JavaScript library.

• The purpose of jQuery is to make it much easier to use JavaScript on your website.
• jQuery takes a lot of common tasks that require many lines of JavaScript code to accomplish and wraps them into methods that you can call with a single line of code.
• jQuery also simplifies a lot of the complicated things from JavaScript, like AJAX calls and DOM manipulation.

2. Does jQuery work for both HTML and XML Documents?

Yes, jQuery works for both HTML and XML documents. It provides a unified API to traverse and manipulate both HTML and XML structures.

• jQuery uses its selectors and methods like .find(), .text(), and .attr() to access elements in both types of documents.
• However, for XML documents, jQuery treats them as a generic tree structure, and you can traverse through XML tags and attributes in a similar way as HTML elements.

3. What are jQuery Selectors?

jQuery selectors allow you to select and manipulate HTML element(s).

• jQuery selectors are used to “find” (or select) HTML elements based on their name, id, classes, types, attributes, values of attributes and much more.
• It’s based on the existing CSS Selectors, and in addition, it has some own custom selectors.
• All selectors in jQuery start with the dollar sign and parentheses: $().

4. What are the advantages of using jQuery?

• Ease of use– it is more easy to use than the standard javascript and other libraries.
• Large library – It has a lot of functions compared to javascript.
• Strong opensource community – there are a lot of plugins available for the faster development of the applications.
• Great documentation and tutorials – the jQuery website has plenty of tutorials that are required for the beginners.
• Ajax support – They let you develop the templates easily.

5. What are the jQuery methods to provide effects?

jQuery offers several methods to provide effects for HTML elements. Some of the most commonly used ones include:

• toggle() : Toggles between showing and hiding an element.
• fadeIn() : Gradually fades in an element.
• fadeOut() : Gradually fades out an element.
• slideDown() : Slides an element down to make it visible.
• fadeToggle() : Toggles the visibility of an element with a fade effect.
• .animate(): Performs a custom animation on a set of CSS properties over a specified duration.
• .slideUp(): Slides an element up to hide it.
• .show(): Displays an element that was hidden using .hide().
• .hide(): Hides the selected elements.

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

In jQuery, the empty(), remove(), and detach() methods are used to manipulate DOM elements, but they have different behaviors:

• empty(): Removes all child elements and text from the selected element but keeps the element itself in the DOM. Useful when you want to clear the content of an element but keep the element in place for future manipulation.

$('#container').empty(); 

• remove(): Completely removes the selected element from the DOM, including all its children and data attached to it. Useful when you want to completely remove an element and all its content from the DOM, including event handlers and data.

$('#item').remove(); 

• detach(): Similar to remove(), but it keeps all event handlers and data associated with the removed elements. Useful when you want to remove an element temporarily but may wish to reattach it later with its event handlers and data intact.

var detachedElement = $('#item').detach(); 
$('#container').append(detachedElement);

7. Is jQuery a JavaScript or JSON library file?

jQuery is a JavaScript library, not a JSON (JavaScript Object Notation) library file.

• JavaScript: jQuery is written in JavaScript and can be used to manipulate HTML and interact with the DOM (Document Object Model) using JavaScript syntax.
• JSON: JSON is a data format used for structuring data in a readable format for humans and machines, but jQuery is not related to JSON itself; however, jQuery can be used to work with JSON data (like parsing and making Ajax requests).

8. What are the different Ajax functions available in jQuery?

jQuery provides several methods to work with AJAX (Asynchronous JavaScript and XML) for making asynchronous requests to the server. Below are the most commonly used AJAX functions

9. Mention the compatible operating systems with jQuery.

jQuery is a JavaScript library that works across all operating systems as long as the browser supports JavaScript. jQuery’s compatibility depends on the browser, not the operating system. It’s compatible with modern browsers on

• Windows: Chrome, Firefox, Edge, Safari, Opera
• macOS: Safari, Chrome, Firefox, Edge, Opera
• Linux: Chrome, Firefox, Opera, Chromium
• iOS: Safari, Chrome, Firefox, Opera
• Android: Chrome, Firefox, Opera, Samsung Internet

10. How to include the jQuery library in an ASP.NET project?

To include jQuery in an ASP.NET project, you can use one of these methods:

• CDN (Content Delivery Network): Add this script tag in your HTML or Razor page.

 <script src="https://code.jquery.com/jquery-3.6.0.min.js"></script>

• Local File: Download jQuery and save it in the Scripts folder.

<script src="~/Scripts/jquery-3.6.0.min.js"></script>

• NuGet Package: Install jQuery via NuGet in Visual Studio.

<script src="~/Scripts/jquery-3.6.0.min.js"></script>

11. What is the use of the param() method in jQuery?

The param() method in jQuery is used to is used to convert a set of key/value pairs into a query string format, which is typically used in URL encoding or when sending data in an HTTP request, especially with AJAX. It converts an object or array into a query string.

Syntax

$.param( object, trad )

Parameters: This method accepts two parameters as mentioned above and described below:

• object: It is a mandatory parameter that is used to specify an array or object to serialize.
• trad: It is an optional parameter and is used to specify whether or not to use the traditional style of param serialization.

12. How to check the version of jQuery?

To check the version of jQuery in your project, we can use one of the following methods:

Method 1: Using $.fn.jquery

console.log($.fn.jquery);

Method 2: Using jQuery.fn.jquery

console.log(jQuery.fn.jquery);

Method 3: Using Browser Developer Tools

• Open the Developer Tools in your browser (press F12 or Ctrl+Shift+I).
• Go to the Console tab.
• Type $.fn.jquery and press Enter to view the version.

13. What is jQuery Connect?

jQuery Connect isn’t an official jQuery feature, but it could refer to:

Event Binding: Using jQuery to “connect” events (like click, hover) to elements.

$("#myButton").click(function() { alert("Button clicked!"); });

Integration with External Resources: Connecting jQuery to APIs or backend services via AJAX.

$.ajax({ url: 'https://api.example.com', method: 'GET' });

14. Difference between find() and children() methods?

15. How does jQuery handle errors?

jQuery provides several methods for error handling:

AJAX Error Handling: Use error, fail, or done to handle AJAX request failures.

$.ajax({
    url: 'example.com',
    success: function(response) { console.log(response); },
    error: function(xhr, status, error) { console.log(status, error); }
});

$.error(): Triggers a custom error message.

$.error("Custom error message");

Global Error Handling: Use $(document).ajaxError() to handle all AJAX errors globally.

$(document).ajaxError(function(event, xhr, settings, error) { console.log(error); });

JavaScript Errors: Use try…catch to handle general errors.

try { someUndefinedFunction(); } catch (e) { console.log(e.message); }

16. What are the different ways to store data in jQuery?

We can store data in jQuery using the following methods

• Local storage (localStorage.setItem())
• Session storage (sessionStorage.setItem())
• Cookies (document.cookie)
• jQuery .data() method

17. How does jQuery handle case-insensitive attribute selectors?

jQuery supports case-insensitive attribute selectors using the i flag. This allows matching elements regardless of the case.

$("[name='MyInput' i]").css("background-color", "yellow");

This will select elements with the name attribute as “MyInput”, “myinput”, “MYINPUT”, etc., and apply the style.

18. What is the difference between $(this) and $(event.target)?

19. What is chaining in jQuery?

Chaining in jQuery allows you to perform multiple actions on the same set of elements, one after another, in a single line of code. This is made possible because most jQuery methods return the jQuery object itself, enabling you to chain multiple methods together.

$("#myDiv")
    .css("color", "red")        // Change text color to red
    .slideUp(1000)             // Slide up over 1 second
    .slideDown(1000)       // Slide down over 1 second
    .fadeOut(500);           // Fade out over 0.5 second

20. Explain $.when() and $.then() in jQuery.

This JQuery.when() method in JQuery gives a way to execute callback functions depending on zero or more Thenable objects, which usually are Deferred objects that represent asynchronous events.

Syntax

$.when(promise1, promise2, ...).done(function(results) {

});

The $.then() method is used to chain actions or handle the results when a Promise (or deferred object) resolves successfully. It allows chaining actions after the completion of a promise and gives more control over handling the results of asynchronous tasks.

$.ajax("url").then(function(response) {
    console.log(response);
}, function(error) {
    console.log(error);
});

21. What is the purpose of $.extend() method in jQuery?

The $.extend() method in jQuery is used to merge two or more objects into one. It is primarily used to copy properties from one or more source objects to a target object. This method can be very helpful when you want to combine default options with user-provided options or merge multiple objects.

• stopPropagation(): Prevents the event from bubbling up the DOM tree.
• preventDefault(): Prevents the default action associated with the event.

Intermediate jQuery Interview Questions

22. What is the difference between .not() and .filter() in jQuery?

Both not(selector) and filter(selector) are used to select elements based on specific conditions, but they are used in different contexts and behave differently.

23. How do you handle form validation using jQuery?

Form validation ensures that the data entered into a form is correct before it is submitted. jQuery provides various ways to handle form validation easily by using built-in methods and custom checks.

HTML Form

<form id="myForm">
    <input type="text" id="username" placeholder="Username">
    <input type="email" id="email" placeholder="Email">
    <input type="password" id="password" placeholder="Password">
    <button type="submit">Submit</button>
</form>
<div id="error-message"></div>

jQuery Validation

$(document).ready(function () {
    $("#myForm").submit(function (event) {
        event.preventDefault();
        var isValid = true;
        var errorMessages = [];

        if ($("#username").val() === "") {
            isValid = false;
            errorMessages.push("Username is required.");
        }

        var email = $("#email").val();
        var emailPattern = /^[a-zA-Z0-9._-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,6}$/;
        if (!email || !emailPattern.test(email)) {
            isValid = false;
            errorMessages.push("Valid email is required.");
        }

        if ($("#password").val().length < 6) {
            isValid = false;
            errorMessages.push("Password must be at least 6 characters.");
        }

        if (!isValid) {
            $("#error-message").html("<ul><li>" + errorMessages.join("</li><li>") + "</li></ul>");
        } else {
            alert("Form submitted successfully!");
        }
    });
});

24. Can you explain about ajaxStart() functions?

The ajaxStart() function in jQuery is triggered when any Ajax request starts. It is used to execute actions before an Ajax request, like showing a loading indicator. It is useful for showing loading indicators or disabling UI elements during Ajax requests.

Syntax

$(document).ajaxStart(function() {
});

25. How do you fade in an element only if it’s hidden?

To fade in an element only if it’s hidden, we can first check the element’s display property using the css() method. If the value is set to none, which indicates that the element is hidden, you can then apply the fadeIn() method to smoothly make it visible.

if (!$("#box").is(":visible")) {
    $("#box").fadeIn();
}

26. What is the purpose of the bind(), live(), and delegate() methods in jQuery?

In jQuery, the bind(), live(), and delegate() methods are used for event handling.

• bind(): Binds event handlers to elements.It directly binds the event handler to the specified element at the time of binding.It only works for elements that exist when the script runs, so it won’t work for elements added dynamically after the page loads.
• live(): Binds events to dynamically added elements (deprecated).The live() method attaches an event handler to all matching elements, including those that are added to the DOM dynamically after the initial page load.
• delegate(): Binds events to parent elements and uses event delegation.It is typically used when you want to handle events for dynamically added elements.You specify the parent element and the child elements you want to listen for events on. When the event occurs on a matching child element, it is handled by the event handler.

27. How do you create and read cookies using jQuery?

Use the jQuery Cookie plugin (or $.cookie() method) to create, read, and delete cookies. For example:

• $.cookie(‘name’, ‘value’); to create.
• $.cookie(‘name’); to read.

28. What are the different ways to select elements in jQuery?

29. Can you explain the ajaxComplete() function?

The ajaxComplete() function in jQuery is an event handler that is triggered when an AJAX request completes (either successfully or with an error). It is called for every AJAX request that completes, no matter what.

• The ajaxComplete() function allows you to run some code after an AJAX request finishes, regardless of whether it succeeded or failed.
• This makes it a useful tool for performing actions like resetting UI elements, showing a loading spinner, or logging statistics after an AJAX request is done.

$(document).ajaxComplete(function(event, xhr, settings) {
});

30. How to append, prepend, and insert content in jQuery?

In jQuery, we can easily append, prepend, and insert content into HTML elements using specific methods.

• append(): Adds content to the end of selected elements.
• prepend(): Adds content to the beginning of selected elements.
• insertBefore(), insertAfter() for inserting content at specific positions.

31. What exactly is a jQuery Data Table plugin?

The jQuery DataTable plugin is a powerful and flexible tool for enhancing HTML tables.

• It provides interactive features like sorting, searching, pagination, and filtering out of the box.
• By transforming standard HTML tables into dynamic, user-friendly data grids.
• It helps improve the user experience for displaying large sets of tabular data.

32. What is event delegation in jQuery?

Event delegation is the practice of binding an event to a parent element rather than directly to individual child elements, making it more efficient and handling dynamically added elements.

• It reduces the number of event handlers by using one for a parent element instead of multiple for each child.
• It works even with elements that are added to the DOM after the page has loaded (e.g., via AJAX or user interaction).

Event delegation in jQuery

33. How to perform an AJAX request in jQuery?

To perform an AJAX request in jQuery, you can use the $.ajax() method, which allows you to send asynchronous HTTP requests to the server and handle the response without refreshing the page. jQuery provides the $.ajax() method for making these requests, offering a wide range of customization options for HTTP requests.

Key Featues

• url: The URL where the request is sent.
• type: Specifies the HTTP request method (GET, POST, etc.).
• data: Data to be sent with the request (used for POST or PUT).
• success: Function to execute if the request succeeds.
• error: Function to execute if the request fails.

34. What is the difference between $.get() and $.post() methods?

Advanced jQuery Interview Questions

35. What is $.proxy() and how is it used?

$.proxy() is used to preserve the this context inside event handlers. This is useful when working with event handlers or callbacks, where the value of this can change, and you need to bind it to a specific context (such as a DOM element or an object).

var obj = {
    message: "Hello",
    showMessage: function () {
        console.log(this.message);
    }
};

$("#btn").on("click", $.proxy(obj.showMessage, obj)); 

36. How do you debounce a function in jQuery?

Debouncing is a technique used to limit the number of times a function is called in response to events that trigger frequently (like scrolling, resizing, keypresses, etc.).

• It ensures that the function is only called after a certain amount of time has passed since the last event was triggered, preventing it from being called too many times in quick succession.
• It reduces unnecessary function calls, improving performance, especially for expensive operations (like API calls or heavy DOM manipulation).
• It prevents overwhelming the user interface with too many changes at once.

function debounce(func, delay) {
    let timer;
    return function () {
        clearTimeout(timer);
        timer = setTimeout(() => func.apply(this, arguments), delay);
    };
}

$(window).on("resize", debounce(function () {
    console.log("Resized!");
}, 500));

37. How do you create a jQuery plugin?

A jQuery plugin is a way to extend the functionality of jQuery by creating reusable functions that can be applied to jQuery objects.

• These plugins allow developers to add custom methods that can be called on jQuery objects, making it easier to encapsulate complex logic and keep the code modular and clean.
• A plugin allows you to separate concerns by encapsulating specific functionality into a self-contained module. This keeps your codebase clean and manageable.
• By using plugins, you can hide the complexity of a specific task or feature inside a simple interface, making it easier for other developers to use.

(function ($) {
    $.fn.changeColor = function (color) {
        this.css("color", color);
        return this;
    };
})(jQuery);

$("p").changeColor("blue");

38. How does jQuery internally work?

jQuery is a fast, small, and feature-rich JavaScript library that simplifies tasks like DOM manipulation, event handling, animation, and AJAX requests.

• jQuery wraps native JavaScript methods and provides a simpler API.
• Uses a combination of JavaScript event delegation and CSS selectors for fast element selection.
• Internally uses document.querySelectorAll() or getElementById() depending on the selector used.

jQuery internally work

39. Why is jQuery still relevant despite modern frameworks like React and Vue?

Reasons Why jQuery Remains Relevant Despite Modern Frameworks

• Simplicity and Ease of Use: jQuery’s syntax is easy to learn and ideal for quick DOM manipulation without the complexity of modern frameworks.
• No Build Tools Needed: Unlike React and Vue, jQuery doesn’t require complex build tools, making it simpler for smaller projects.
• Legacy Support: Many existing websites still rely on jQuery, and it ensures cross-browser compatibility out of the box.
• Lightweight: jQuery is smaller in size compared to React and Vue, making it great for simple websites and fast loading times.
• Rapid Prototyping: jQuery allows for quick implementation of features like animations and event handling, ideal for prototypes.
• Plugins: A rich ecosystem of jQuery plugins makes adding features like carousels, form validation, and more easy without extra coding.
• Quick DOM Manipulation: jQuery offers efficient, concise methods for DOM tasks, unlike more complex React/Vue approaches.
• Interoperability: It can easily be integrated into existing projects and mixed with modern frameworks without a complete rewrite.

40. How to optimize jQuery for performance?

Best Practices for Enhancing jQuery Performance

• Cache Selectors: Store DOM elements in variables to avoid repeated lookups.
• Minimize DOM Manipulation: Batch DOM changes to avoid multiple reflows.
• Use Event Delegation: Bind events to parent elements instead of individual items.
• Reduce Reflows/Repaints: Minimize style changes that trigger layout recalculations.
• Limit Plugins: Only use essential plugins to avoid overhead.
• Prefer Native JavaScript: Use vanilla JavaScript for simple tasks when possible.
• Minify Code: Compress both jQuery and your own code to reduce file sizes.
• Defer jQuery Loading: Load jQuery asynchronously or with defer to avoid blocking page render.

41. What is the difference between $(document).ready() and $(window).on(“load”)?

42. Explain how event bubbling and event capturing work in jQuery.

Event Bubbling and Event Capturing are two phases in the event propagation model in JavaScript and jQuery.

Event bubbling

• The event starts from the target element and moves up to the root document (child → parent).
• It allows parent elements to catch events triggered by child elements.
• Example: If you click a button inside a div, the click event first triggers on the button, and then bubbles up to the parent div, and so on until it reaches document.

Event capturing:

• The event starts from the root document and moves down to the target (parent → child).
• Capturing allows you to catch an event before it reaches the target.
• It’s less commonly used compared to bubbling.

$("#parent").on("click", function () {
    alert("Parent clicked!");
});

$("#child").on("click", function (event) {
    alert("Child clicked!");
    event.stopPropagation(); 
});

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

Yes, it is possible to pause or postpone the execution of $(document).ready() for a period of time using JavaScript’s setTimeout() function.

Delayed Execution with setTimeout: Sometimes you might want to delay certain actions after the page is ready (like animations or API calls), but still, make sure that the DOM is loaded first.

$(document).ready(function () {
    console.log("Document is ready!");

    setTimeout(function () {
        alert("This message appears after a 3-second delay!");
    }, 3000); 
});

Simulating a Loading Delay: A typical use case could be simulating a loading screen. For example, if you’re fetching data from an API and want to show a “loading” message for a set amount of time before displaying the data:

$(document).ready(function () {
    $('#loadingMessage').show();
    setTimeout(function () {
       
        $('#loadingMessage').hide();
        $('#content').fadeIn();
    }, 3000); 
});

44. Explain $.fn and its role in jQuery plugin development.

When developing jQuery plugins, $.fn is used to add new functions to jQuery’s object prototype. This allows you to call these functions on any jQuery object, just like built-in methods like .click() or .hide(). By extending $.fn, you ensure that your custom methods are chainable and behave like native jQuery methods.

• $.fn is a shortcut for jQuery.prototype.
• It is used to extend jQuery and create custom plugins.

Example of a simple jQuery plugin:=

(function ($) {
    $.fn.highlight = function (color) {
        this.css("background-color", color);
        return this;
    };
})(jQuery);

$("p").highlight("yellow");

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

The .promise() method in jQuery is used to create a promise object that represents the eventual completion or failure of an asynchronous operation.

• It provides a way to handle the results of one or more asynchronous operations and chain the responses once all the asynchronous tasks are completed.
• It’s particularly useful when you have multiple operations that need to be completed before executing subsequent code.
• It returns a Promise object, which can be used to define success or failure callbacks using .done(), .fail(), and .always() methods.
• Often used in conjunction with animation or DOM manipulation methods to ensure certain actions are completed before continuing.

var promise = $(selector).promise(type);

46. What are the key differences between jQuery $.each() and JavaScript’s forEach()

47. How does jQuery handle asynchronous operations?

jQuery provides a robust set of tools for handling asynchronous operations, allowing developers to manage delayed or non-blocking tasks such as server requests, animations, or timed events.

AJAX: jQuery provides $.ajax(), $.get(), and $.post() for making asynchronous HTTP requests without reloading the page.

$.ajax({
    url: 'example.com',
    success: function(response) { console.log(response); },
    error: function(xhr, status, error) { console.log(status, error); }
});

Deferred and Promises: The $.Deferred() object and .then() method manage asynchronous operations by handling success and error cases.

var deferred = $.Deferred();
setTimeout(function() {
    deferred.resolve("Task completed");
}, 2000);
deferred.done(function(result) {
    console.log(result);
});

.ready(): Ensures that code runs only after the DOM is fully loaded.

$(document).ready(function() {
    console.log("Document is ready!");
});

Animations: jQuery’s animation methods like .fadeIn() are asynchronous, with callback functions to run once the animation is complete.

$("#element").fadeIn(1000, function() {
    console.log("Animation complete!");
});

Event Handlers: User interactions (e.g., clicks) trigger asynchronous event handlers without blocking the rest of the script.

$("#button").click(function() {
    console.log("Button clicked!");
});

48. How do you ensure memory efficiency while using jQuery?

To maintain memory efficiency in your jQuery code, it’s crucial to follow best practices that minimize memory leaks and optimize performance. Below are key strategies to ensure efficient memory usage when working with jQuery

• Avoid Global Variables : Use local variables inside functions whenever possible. If global variables are necessary, consider using closures to encapsulate them.
• Unbind Event Handlers : Always use .off() to unbind event handlers when they are no longer needed, especially in dynamically created content.
• Use .remove() to Clean Up DOM Elements : When removing elements from the DOM, use .remove() to ensure the element and its associated events and data are properly cleaned up.
• Limit jQuery Selectors : Be specific with your selectors and try to avoid searching the entire DOM. Cache frequently accessed elements in variables.
• Use $.data() and $.removeData() Properly : If you no longer need the stored data, call $.removeData() to ensure memory is freed.
• Be Careful with setInterval() and setTimeout() : Always use clearInterval() or clearTimeout() to stop periodic actions when they are no longer required.
• Optimize DOM Manipulations : Batch DOM manipulations by using .append(), .prepend(), or .html() in bulk, rather than manipulating individual elements repeatedly.

49. What is the difference between event.preventDefault() and event.stopPropagation()?

Both event.preventDefault() and event.stopPropagation() are used to control event behavior, but they serve different purposes:

50. How do you optimize jQuery performance in large-scale applications?

To improve jQuery performance, consider the following optimization techniques:

Cache Selectors: Store frequently used elements in variables instead of querying the DOM multiple times.

var $btn = $("#myButton");
$btn.click(function() {
    $btn.text("Clicked!");
});

Use Event Delegation: Attach event handlers to parent elements instead of individual child elements.

$(document).on("click", ".dynamic-button", function() {
    alert("Button Clicked!");
});

Minimize DOM Manipulation: Batch changes to the DOM instead of modifying it repeatedly.

var items = "";
for (var i = 0; i < 100; i++) {
    items += "<li>Item " + i + "</li>";
}
$("#list").html(items);

• Use .on() Instead of .bind() or .live(): .on() improves event handling performance.
• Remove Unused Elements & Data: Use .remove() and .empty() when elements are no longer needed.

Top 50+ jQuery Interview Questions and Answers – 2025