Interview Questions for JQuery

JQuery is a fast and lightweight JavaScript library that simplifies tasks like HTML document traversal, manipulation, event handling, and AJAX.

You can include JQuery by adding a <script> tag in the HTML file linking to the JQuery CDN or a downloaded JQuery file. For example:

The $ symbol is an alias for the JQuery function. It is a shorthand way to call JQuery methods.

The .off() method is used to remove event handlers that have been attached with .on().

The $(document).ready() function in JQuery is executed when the DOM is fully loaded, but before other resources like images and CSS are completely loaded. On the other hand, window.onload waits for all resources, including images and CSS, to be loaded before executing the code.

In JQuery, the this keyword refers to the DOM element that is currently being acted upon in the event handler. It allows you to perform actions on the element without having to reselect it.

Selectors are patterns used to match DOM elements. For example, $('p') selects all paragraph elements, and $('.className') selects all elements with the given class name.

JQuery supports a wide range of selectors including ID selectors (#id), class selectors (.class), element selectors (element), and more advanced selectors like attribute selectors and pseudo-selectors.

You can use methods like .click(), .bind(), .on(), etc., to bind events to elements. For example, $('#button').click(function() { /* code */ }); binds a click event to an element with the ID of ‘button’.

JavaScript is a programming language, whereas JQuery is a library built on top of JavaScript. JQuery simplifies tasks such as DOM manipulation and event handling, making it easier and faster to develop web applications.

You can use the $.ajax() method to make AJAX calls. It allows you to specify options like the URL, data type, and success and error callbacks.

The animate() method allows you to create custom animations. You can animate CSS properties over a specified duration.

JQuery provides various traversal methods like .parent(), .children(), .next(), .prev(), etc., to navigate through the DOM.

Chaining allows you to execute multiple JQuery methods on the same set of elements, in a single line. For example, $('p').hide().addClass('hidden').fadeIn();

You can use methods like .append(), .prepend(), .remove(), and .empty() to add or remove elements.

The data() method allows you to attach data to, or fetch data from, DOM elements. This can be useful for storing additional information without modifying the DOM.

You can use methods like .hide(), .show(), or .toggle() to hide, show, or toggle the visibility of elements.

JQuery plugins are reusable pieces of code that extend the functionality of JQuery. You can use a plugin by including its JavaScript file after including the JQuery library.

• Advantages: Easy to use, large community, lots of plugins, simplifies complex tasks like AJAX and DOM manipulation.
• Disadvantages: Adds to page load time, may lead to over-dependency, not always necessary for simple tasks.

Methods like .val(), .prop(), and .attr() can be used to get or set the values and attributes of form elements. You can also use .submit() it to handle form submissions.

The .attr() method can be used to get or set attributes. For example, $('img').attr('src', 'image.jpg') sets the source attribute of an image element.

The each() method is used to loop through elements in a JQuery object. It allows you to apply the same set of actions to all elements in the selection.

Event delegation allows you to attach a single event listener to a parent element, which will fire for all descendants that match a given selector. This is useful for elements that are dynamically added to the DOM.

.bind(): Attaches events to elements that are currently in the DOM.

.live(): Deprecated method that is used to attach events to current and future elements in the DOM.

.on(): Replaces both .bind() and .live(), and can be used for attaching events to current and future elements.