"jQuery is a fast and concise JavaScript Library that simplifies HTML document traversing, event handling, animating, and Ajax interactions for rapid web development. jQuery is designed to change the way that you write JavaScript." - jQuery.com

jQuery is a cross-browser JavaScript library designed to simplify the client-side scripting of HTML. It was released in January 2006 at BarCamp NYC by John Resig. Used by over 49% of the 10,000 most visited websites, jQuery is the most popular JavaScript library in use today.

jQuery is free, open source software, dual-licensed under the MIT License or the GNU General Public License, Version 2. jQuery's syntax is designed to make it easier to navigate a document, select DOM elements, create animations, handle events, and develop Ajax applications. jQuery also provides capabilities for developers to create plug-ins on top of the JavaScript library. This enables developers to create abstractions for low-level interaction and animation, advanced effects and high-level, theme-able widgets. The modular approach to the jQuery framework allows the creation of powerful and dynamic web pages and web applications.

jQuery contains the following features:

  • DOM element selections using the cross-browser open source selector engine Sizzle, a spin-off out of the jQuery project
  • DOM traversal and modification (including support for CSS 1-3)
  • Events
  • CSS manipulation
  • Effects and animations
  • Ajax
  • Extensibility through plug-ins
  • Utilities - such as user agent information, feature detection
  • Compatibility methods that are natively available in modern browsers but need fallbacks for older ones - For example the inArray() and each() functions.
  • Cross-browser support
jQuery has two usage styles:
  • via the $ function, which is a factory method for the jQuery object. These functions, often called commands, are chainable; they all return jQuery objects
  • via $.-prefixed functions. These are utility functions which do not work on the jQuery object per se.

Typically, access to and manipulation of multiple DOM nodes begins with the $ function being called with a CSS selector string, which results in a jQuery object referencing matching elements in the HTML page. This node set can be manipulated by calling instance methods on the jQuery object, or on the nodes themselves.