JQuery

Did You Know?

• The jQuery library is typically distributed as a single JavaScript file and can be included from a local copy or from public servers, including CDNs hosted by MaxCDN, Google, and Microsoft.
• QUnit, a test automation framework developed by the jQuery team, is used to test the jQuery project and can test any generic JavaScript code.
• GitHub removed jQuery from its pages in 2018, partly because cross-browser compatibility is no longer as much of an issue and most of jQuery can be replaced with modern web standards.

Overview

jQuery is a Document Object Model (DOM) manipulation library. The DOM is a tree-structure representation of all elements of a Web page, and jQuery simplifies the syntax for finding, selecting, and manipulating these elements. For example, jQuery can find an element with a certain property, change its attributes, or make it respond to an event. jQuery also provides a paradigm for event handling where event assignment and callback function definition occur in a single step. The principles of developing with jQuery include separation of JavaScript and HTML, brevity and clarity through chainable functions and shorthand names, elimination of cross-browser incompatibilities, and extensibility through easily added plugins.

History

jQuery was created in January 2006 at BarCamp NYC by John Resig, influenced by Dean Edwards' cssQuery library. It is maintained by a team led by Timmy Willison, with the Sizzle selector engine led by Richard Gibson. Originally licensed under CC BY-SA 2.5, it was relicensed to the MIT License in 2006, then dual-licensed under GPL and MIT until 2012 when the GPL was dropped. In 2015, jQuery was used on 62.7% of the top 1 million websites, rising to 80% of the top 1 million in 2019 and 77.8% of the top 10 million in 2021.

Features

jQuery includes DOM element selections using the Sizzle selector engine, DOM manipulation based on CSS selectors, events, effects and animations, Ajax, Deferred and Promise objects for asynchronous processing, JSON parsing, extensibility through plugins, utilities such as feature detection, and compatibility methods for older browsers. jQuery 3.0 and newer supports current minus one versions of Firefox, Chrome, Safari, and Edge, as well as Internet Explorer 9 and newer, iOS 7 and newer, and Android 4.0 and newer.

Interface

jQuery provides static utility functions and jQuery object methods, both accessed through the main identifier jQuery or its alias $. The jQuery function is a factory for creating a jQuery object representing one or more DOM nodes. Methods on jQuery objects are chainable, as each method returns a jQuery object. Access typically begins with calling $ with a CSS selector string, returning a jQuery object referencing matching elements.

Static methods like $.ajax() do not act on a jQuery object. jQuery provides a $.noConflict() function to relinquish control of the $ name when used with other libraries. Initialization code is placed in $(handler), triggered when the browser finishes constructing the DOM. Historically, $(document).ready(callback) was used, but since jQuery 3.0, $(handler) is encouraged. Method chains allow operations like selecting elements, registering event handlers, and adding classes in one line.