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Top Interview Questions
jQuery is a fast, lightweight, and widely used JavaScript library that was created to simplify client-side web development. Introduced in 2006 by John Resig, jQuery quickly became popular among developers because it made common JavaScript tasks easier and more efficient. At a time when writing JavaScript often required long and complex code, jQuery provided a simpler syntax that allowed developers to achieve the same results with fewer lines of code. Although modern JavaScript has evolved significantly, jQuery still holds an important place in the history and development of the web.
One of the main reasons for jQuery’s popularity is its ability to handle cross-browser compatibility issues. In the early days of web development, different browsers interpreted JavaScript in slightly different ways. This caused many problems for developers, who had to write separate code for each browser. jQuery solved this problem by providing a consistent interface that worked the same way across major browsers such as Chrome, Firefox, Safari, and Internet Explorer. By using jQuery, developers could write code once and trust that it would work reliably on different platforms.
jQuery is especially known for simplifying DOM (Document Object Model) manipulation. The DOM represents the structure of a webpage, including elements like headings, paragraphs, buttons, and images. With plain JavaScript, selecting and modifying these elements can be verbose and confusing, especially for beginners. jQuery introduced a powerful selector system inspired by CSS selectors, making it easy to target elements on a page. For example, developers can quickly select elements by their ID, class, or type and then change their content, style, or behavior with just a few lines of code.
Another important feature of jQuery is event handling. Events occur when users interact with a webpage, such as clicking a button, hovering over an image, or submitting a form. jQuery provides simple methods to attach event handlers to elements, making it easier to respond to user actions. Instead of writing complex JavaScript code to listen for events, developers can use straightforward jQuery functions. This helps create interactive and responsive websites that feel smooth and user-friendly.
Animations and visual effects are another area where jQuery excels. Before jQuery, creating animations often required advanced JavaScript knowledge or external tools. jQuery made animations accessible by offering built-in methods for effects such as fading, sliding, hiding, and showing elements. These effects can be applied with minimal effort, allowing developers to enhance the visual appeal of their websites. While modern CSS and JavaScript now provide more advanced animation options, jQuery played a key role in making web animations more common and easier to implement.
jQuery also simplified AJAX (Asynchronous JavaScript and XML) requests. AJAX allows web pages to communicate with servers in the background without reloading the entire page. This makes applications faster and more interactive, such as loading new content dynamically or submitting forms without refreshing. jQuery offers easy-to-use methods for making AJAX calls, handling responses, and managing errors. This helped many developers create more dynamic web applications at a time when AJAX was still considered complex and difficult to implement.
As jQuery grew in popularity, a large ecosystem of plugins emerged. These plugins extended jQuery’s functionality and allowed developers to add advanced features to their websites quickly. Plugins were available for image sliders, date pickers, form validation, charts, and much more. Instead of building everything from scratch, developers could rely on community-created plugins, saving time and effort. This strong community support contributed significantly to jQuery’s widespread adoption.
Despite its many advantages, jQuery is not without limitations. As JavaScript evolved, new features were added to the language that reduced the need for external libraries. Modern JavaScript, often referred to as “vanilla JavaScript,” now includes built-in methods for tasks that once required jQuery. Additionally, modern frameworks such as React, Angular, and Vue.js introduced new ways of building web applications using components and virtual DOMs. These approaches often offer better performance and scalability for large projects compared to jQuery.
Because of these changes, jQuery is no longer the first choice for many new web applications. However, it is still widely used, especially in older projects and simpler websites. Many existing websites rely heavily on jQuery, and maintaining or updating them requires knowledge of the library. For this reason, understanding jQuery remains valuable for web developers, particularly those working with legacy systems.
From a learning perspective, jQuery is often considered beginner-friendly. Its simple syntax and clear methods make it easier for newcomers to understand how JavaScript interacts with web pages. By learning jQuery, students can quickly see how events, animations, and dynamic content work together. This can build confidence and provide a solid foundation before moving on to more advanced JavaScript concepts or frameworks.
In conclusion, jQuery has played a crucial role in shaping modern web development. It simplified JavaScript, solved cross-browser issues, and made interactive websites more accessible to developers of all skill levels. While newer technologies have reduced its importance in cutting-edge projects, jQuery’s influence is undeniable. It helped pave the way for modern JavaScript frameworks and improved development practices. Even today, jQuery remains a valuable tool and an important part of web development history, making it worth learning and understanding for anyone interested in the field.
Answer:
jQuery is a fast, lightweight, and feature-rich JavaScript library that simplifies:
HTML DOM manipulation
Event handling
Animations
AJAX calls
It follows the principle:
👉 “Write less, do more”
Answer:
We use jQuery to:
Reduce JavaScript code
Handle cross-browser compatibility
Simplify DOM manipulation
Perform AJAX easily
Create animations quickly
Answer:
| jQuery | JavaScript |
|---|---|
| JavaScript library | Programming language |
| Shorter syntax | More code |
| Cross-browser support | Browser dependent |
| Easy DOM handling | Complex DOM handling |
Answer:
<script src="https://code.jquery.com/jquery-3.6.0.min.js"></script>
<script src="jquery.js"></script>
$(document).ready()?Answer:
It ensures the DOM is fully loaded before executing jQuery code.
$(document).ready(function () {
console.log("Page loaded");
});
Shortcut:
$(function () {
console.log("Ready");
});
$ mean in jQuery?Answer:
$ is a shortcut for jQuery function.
$("p").hide();
Answer:
Selectors are used to select HTML elements.
Element: $("p")
ID: $("#id")
Class: $(".class")
Attribute: $("[type='text']")
Answer:
$("h1, h2, h3").css("color", "red");
Answer:
Events are actions performed by users.
click()
dblclick()
mouseenter()
keypress()
submit()
$("button").click(function () {
alert("Clicked!");
});
Answer:
Handling events for dynamic elements using a parent.
$("ul").on("click", "li", function () {
alert($(this).text());
});
on() and click()?Answer:
| click() | on() |
|---|---|
| For existing elements | For dynamic elements |
| Single event | Multiple events |
Answer:
Effects add animations.
hide()
show()
toggle()
fadeIn()
fadeOut()
slideUp()
slideDown()
$("#box").fadeOut();
Answer:
Calling multiple methods on the same element.
$("#box").css("color", "red").slideUp().slideDown();
Answer:
AJAX allows data exchange without page reload.
$.ajax({
url: "data.json",
success: function (result) {
console.log(result);
}
});
GET and POST in AJAX?Answer:
| GET | POST |
|---|---|
| Data in URL | Data in body |
| Less secure | More secure |
| Limited data | Large data |
.html() vs .text()?Answer:
| html() | text() |
|---|---|
| Gets HTML | Gets text |
| Can insert tags | Plain text |
.val()?Answer:
Used to get/set form input values.
let name = $("#name").val();
.css()?Answer:
Used to apply styles.
$("p").css("color", "blue");
.addClass() and .removeClass()?Answer:
$("#box").addClass("active");
$("#box").removeClass("active");
.toggleClass()?Answer:
Adds/removes class automatically.
$("#box").toggleClass("active");
.append() vs .prepend()?Answer:
| append() | prepend() |
|---|---|
| Adds at end | Adds at beginning |
.remove() vs .empty()?Answer:
| remove() | empty() |
|---|---|
| Removes element | Removes content |
.attr() vs .prop()?Answer:
| attr() | prop() |
|---|---|
| HTML attribute | DOM property |
each()?Answer:
Loops through elements.
$("li").each(function () {
console.log($(this).text());
});
noConflict()?Answer:
Avoids conflict with other libraries.
$.noConflict();
.data()?Answer:
Stores custom data.
$("#box").data("id", 101);
.find()?Answer:
Finds child elements.
$("#parent").find("p");
.closest()?Answer:
Finds nearest ancestor.
.clone()?Answer:
Copies elements.
$("#box").clone().appendTo("body");
Answer:
A library built on jQuery for UI components like:
Datepicker
Dialog
Drag & Drop
Answer:
jQuery chaining allows you to call multiple methods on the same element in a single statement.
$("#box").css("color", "red").slideUp(500).slideDown(500);
👉 Improves code readability and performance.
.hide() and .css("display","none")?Answer:
| .hide() | css("display","none") |
|---|---|
| jQuery method | CSS property |
| Supports animation | No animation |
| Can use speed | Instant |
.fadeToggle()?Answer:
It toggles fade in and fade out effects.
$("#box").fadeToggle(1000);
.slideToggle()?Answer:
Slides element up or down based on visibility.
$("#menu").slideToggle();
.append() and .after()?Answer:
| append() | after() |
|---|---|
| Inside element | Outside element |
| At end | After element |
.before()?Answer:
Adds content before the selected element.
$("#item").before("<p>New</p>");
.detach()?Answer:
Removes elements but keeps data and events.
var el = $("#box").detach();
.remove() and .detach()?Answer:
| remove() | detach() |
|---|---|
| Removes permanently | Can be reused |
| Data lost | Data retained |
.wrap()?Answer:
Wraps HTML around an element.
$("p").wrap("<div class='wrapper'></div>");
.unwrap()?Answer:
Removes parent wrapper.
.wrapAll()?Answer:
Wraps all selected elements together.
.wrapInner()?Answer:
Wraps content inside element.
.serialize()?Answer:
Converts form data into query string.
$("form").serialize();
.serializeArray()?Answer:
Returns form data as an array of objects.
.ajaxSetup()?Answer:
Sets default AJAX settings.
$.ajaxSetup({
timeout: 3000
});
.get() and .post()?Answer:
Shorthand AJAX methods.
$.get("url", callback);
$.post("url", data, callback);
.load()?Answer:
Loads data into an element.
$("#result").load("data.html");
Answer:
Callback executes after animation completes.
$("#box").hide(1000, function () {
alert("Hidden");
});
.stop()?Answer:
Stops animation queue.
$("#box").stop();
Answer:
Animations are stored and executed in sequence.
.delay()?Answer:
Adds delay between animations.
$("#box").delay(1000).fadeOut();
.hover()?Answer:
Handles mouse enter and leave.
$("#box").hover(
function () { $(this).addClass("in"); },
function () { $(this).removeClass("in"); }
);
.trigger()?Answer:
Manually triggers an event.
$("#btn").trigger("click");
.off()?Answer:
Removes event handlers.
$("#btn").off("click");
.one()?Answer:
Event executes only once.
$("#btn").one("click", function () {
alert("Only once");
});
.index()?Answer:
Returns index of element.
.hasClass()?Answer:
Checks if class exists.
$("#box").hasClass("active");
.is()?Answer:
Checks element state.
$("#checkbox").is(":checked");
.parents() vs .parent()?Answer:
| parent() | parents() |
|---|---|
| Immediate parent | All ancestors |
.children() vs .find()?Answer:
| children() | find() |
|---|---|
| Direct children | All descendants |
Answer:
if ($("#name").val() === "") {
alert("Name required");
}
$("#btn").prop("disabled", true);
$("#check").is(":checked");
$("#dropdown").val();
$("#img").attr("src", "new.jpg");
Answer:
jQuery is a JavaScript library built on top of the browser DOM API.
Internally it:
Uses the Sizzle selector engine to parse CSS selectors
Wraps DOM elements inside a jQuery object
Provides chainable APIs
Normalizes browser differences
Example:
$(".box") // returns a jQuery object, not a DOM element
Answer:
| jQuery Object | DOM Object |
|---|---|
| Wrapper around DOM | Actual DOM node |
| jQuery methods | Native methods |
$(el) |
document.getElementById() |
Conversion:
let dom = $("#id")[0];
let jq = $(dom);
Answer:
Sizzle is jQuery’s CSS selector engine that:
Parses complex selectors
Works across browsers
Optimizes element lookup
Answer:
Event delegation uses event bubbling to handle events at a parent level.
$("#list").on("click", "li", function () {
$(this).addClass("active");
});
Better performance
Supports dynamically added elements
.on() vs .bind() vs .live()Answer:
| Method | Status | Supports Dynamic |
|---|---|---|
| live() | ❌ deprecated | Yes |
| bind() | ❌ deprecated | No |
| on() | ✅ recommended | Yes |
Answer:
Each jQuery method returns the same jQuery object, enabling chaining.
$("#box").addClass("x").fadeOut().fadeIn();
Answer:
jQuery:
Normalizes DOM methods
Handles event differences
Fixes AJAX inconsistencies
Abstracts CSS quirks
Answer:
AJAX stages:
beforeSend
send request
success
error
complete
$.ajax({
beforeSend(){},
success(){},
error(){},
complete(){}
});
$.ajax() vs $.get() vs $.post()Answer:
| ajax() | get()/post() |
|---|---|
| Full control | Shortcut |
| More config | Limited config |
| Used for complex cases | Simple calls |
Answer:
$(document).ajaxError(function (e, xhr) {
console.log(xhr.status);
});
$.Deferred()?Answer:
Deferred is jQuery’s promise-like object for async flow control.
let d = $.Deferred();
d.resolve("Done");
Answer:
| Deferred | Promise |
|---|---|
| Mutable | Immutable |
| Older | Standard |
| jQuery specific | Native |
.queue() and .dequeue()Answer:
Used to manage animation or custom queues.
Answer:
jQuery:
Automatically cleans up events on .remove()
Prevents memory leaks
Uses internal data cache
.remove() vs .detach() vs .empty()Answer:
| Method | Removes Element | Keeps Data |
|---|---|---|
| remove() | Yes | ❌ |
| detach() | Yes | ✅ |
| empty() | ❌ | N/A |
.attr() vs .prop() (real-world)Answer:
.prop() for dynamic states (checked, disabled)
.attr() for static HTML attributes
.data() internalsAnswer:
Stores data in jQuery’s internal cache, not directly in DOM.
Answer:
Best practices:
Cache selectors
Use ID selectors
Avoid universal selectors
Limit DOM traversal
let $el = $("#box");
Answer:
Use document fragments
Minimize reflows
Batch DOM updates
Detach elements
Answer:
$("#btn").on("click.myEvent", handler);
$("#btn").off("click.myEvent");
Answer:
$.fn.myPlugin = function () {
return this.each(function () {
$(this).addClass("plugin");
});
};
Answer:
$("#btn").off("click").on("click", handler);
.clone(true)Answer:
Copies element with events and data.
.end()?Answer:
Reverts to previous selection in chaining.
.closest() differ from .parents()?Answer:
.closest() → first match
.parents() → all ancestors
.filter() vs .find()Answer:
filter() narrows selection
find() searches descendants
Answer:
Uses:
Timers
Inline styles
requestAnimationFrame (modern)
Answer:
Hooks allow modifying default behavior (cssHooks, attrHooks).
Answer:
Browser DevTools
Breakpoints
console.log
jQuery debug build
Answer:
Yes, in:
Legacy systems
CMS platforms
Quick DOM tasks
But modern frameworks often replace it.
Answer:
jQuery uses callbacks, Deferred, and Promises for async tasks.
AJAX calls are non-blocking.
You can chain multiple async operations using .then().
Example:
$.ajax("data.json")
.done(function(data){ console.log(data); })
.fail(function(err){ console.log(err); });
.ajax(), .get(), .post(), and .getJSON()| Method | Use Case | Notes |
|---|---|---|
| $.ajax() | Complex requests | Full control (headers, timeout, callbacks) |
| $.get() | Simple GET | Shortcut |
| $.post() | POST requests | Shortcut |
| $.getJSON() | GET JSON only | Parses JSON automatically |
$.when() and $.Deferred()Answer:
$.Deferred() allows creating custom promises.
$.when() is used to wait for multiple Deferred objects.
Example:
$.when($.ajax("/data1"), $.ajax("/data2")).done(function(a,b){
console.log(a[0], b[0]);
});
Answer:
Memory leaks occur if DOM elements are removed without cleaning event handlers.
jQuery helps by:
.remove() cleans associated events
.off() detaches events
.empty() clears content and memory
Tip: Avoid global references to DOM elements.
.on() vs .delegate()| Method | Support | Notes |
|---|---|---|
| .delegate() | Deprecated | Attach events to descendants |
| .on() | Recommended | Handles both existing & future elements |
$("#parent").on("click", ".child", function(){});
.promise() in jQueryAnswer:
.promise() returns a promise representing completion of a set of animations or events.
Example:
$("#box").slideUp().slideDown().promise().done(function(){
alert("All animations complete");
});
$("#link").on("click", function(e){
e.preventDefault(); // prevents navigation
});
preventDefault() stops default browser behavior.
stopPropagation() stops event bubbling.
Answer:
Namespaces allow managing events without affecting other handlers.
$("#btn").on("click.myNamespace", handler);
$("#btn").off(".myNamespace");
.prop() and .attr() in depth| Feature | .attr() | .prop() |
|---|---|---|
| Returns HTML attribute | Yes | No |
| Returns current DOM state | No | Yes |
| Example | $("input").attr("checked") | $("input").prop("checked") |
Use .prop() for boolean properties like checked, disabled, selected.
$.fn and jQuery pluginsAnswer:
$.fn is the prototype for all jQuery objects.
You can extend jQuery by adding methods to $.fn.
Example:
$.fn.highlight = function(color){
return this.css("background-color", color);
};
$("p").highlight("yellow");
.clone(true) vs .clone(false)| Method | Clones Events/Data |
|---|---|
| .clone(true) | Yes |
| .clone(false) | No |
jQuery uses setInterval or requestAnimationFrame (modern) internally.
Animations are queued.
.stop() can halt animations mid-way.
.dequeue() and .queue() manage animation sequences.
Example:
$("#box").animate({height: "200px"}, 1000);
.wrap(), .wrapAll(), .wrapInner()| Method | Description |
|---|---|
| .wrap() | Wraps each element individually |
| .wrapAll() | Wraps all selected elements together |
| .wrapInner() | Wraps content inside an element |
Uses ID selectors first.
Caches selections in variables.
Uses Sizzle engine.
Minimizes DOM traversal.
Example:
var $list = $("#list"); // Cached
$list.find("li").addClass("active");
.children() and .find()| Method | Scope |
|---|---|
| .children() | Immediate children only |
| .find() | All descendants |
Use .serialize() to convert form data.
Use .serializeArray() for array format.
Validate before submission.
$("form").on("submit", function(e){
e.preventDefault();
var data = $(this).serialize();
$.post("/submit", data);
});
.queue() and custom queues.queue() can queue custom functions on elements.
Useful for sequencing animations or operations.
$("#box").queue(function(next){
$(this).css("background", "red");
next();
});
Use .fail() or .catch() with jQuery Deferred.
Allows better async error management.
$.ajax("/data").done(function(){})
.fail(function(err){ console.log(err); });
Tips:
Replace $() with document.querySelector or querySelectorAll.
Replace .ajax() with fetch().
Replace animations with CSS transitions.
Modularize code instead of chaining too much.
Remove detached DOM elements properly.
Use .off() for event handlers.
Avoid global jQuery references.
Cache DOM selections.
