JQuery

What is jQuery?

jQuery is a fast, small, and feature-rich JavaScript library. It makes things like HTML document traversal and manipulation, event handling, animation, and Ajax much simpler with an easy-to-use API that works across a multitude of browsers. With a combination of versatility and extensibility, jQuery has changed the way that millions of people write JavaScript.

Features

DOM element selections using the multi-browser open source selector engine Sizzle, a spin-off of the jQuery project
DOM traversal and modification (including support for CSS 1–3)
DOM manipulation based on CSS selectors that uses node elements name and node elements attributes (id and class) as criteria to build selectors
Events
Effects and animations
AJAX
JSON parsing
Extensibility through plug-ins
Utilities - such as user agent information, feature detection
Compatibility methods that are natively available in modern browsers but need fall backs for older ones - For example the inArray() and each() functions.
Multi-browser (not to be confused with cross-browser) support.