jQuery is a JavaScript library designed to simplify HTML DOM tree traversal and manipulation, as well as event handling, CSS animations, and Ajax.

[6][7] jQuery's syntax is designed to make it easier to navigate a document, select DOM elements, create animations, handle events, and develop Ajax applications.

This enables developers to create abstractions for low-level interaction and animation, advanced effects and high-level, theme-able widgets.

The set of jQuery core features—DOM element selections, traversal, and manipulation—enabled by its selector engine (named "Sizzle" from v1.3), created a new "programming style", fusing algorithms and DOM data structures.

This style influenced the architecture of other JavaScript frameworks like YUI v3 and Dojo, later stimulating the creation of the standard Selectors API.

jQuery also provides a paradigm for event handling that goes beyond basic DOM element selection and manipulation.

[22] The jQuery library is typically distributed as a single JavaScript file that defines all its interfaces, including DOM, Events, and Ajax functions.

Access to and manipulation of multiple DOM nodes in jQuery typically begins with calling the $ function with a CSS selector string.

This returns a jQuery object referencing all the matching elements in the HTML page.

[27] Typically, jQuery is used by putting initialization code and event handling functions in $(handler).

or Historically, $(document).ready(callback) has been the de facto idiom for running code after the DOM is ready.

In these cases, a statement such as $('#user-email').val() cannot be used for chaining as the return value does not reference a jQuery object.

For example, the below code finds an HTML select element, and creates a new option element with the value VAG and the label Volkswagen, which is then appended to the select menu: It is possible to make Ajax requests (with cross-browser support) with $.ajax() to load and manipulate remote data.

There are thousands of jQuery plug-ins available on the Web[29] that cover a range of functions, such as Ajax helpers, Web services, datagrids, dynamic lists, XML and XSLT tools, drag and drop, events, cookie handling, and modal windows.

[56] Simplifying tasks such as HTML document traversal, animation, and event handling, the stalwart jQuery JavaScript library changed the face of web development.

Nevertheless, the jQuery library, which debuted in August 2006, is now being viewed by some developers as an older technology whose time has passed.