JavaScript library

A JavaScript library is a library of pre-written JavaScript which allows for easier development of JavaScript-based applications, especially for AJAX and other web-centric technologies.

While JavaScript, as first developed by Netscape (and later Mozilla), has long had a presence on the Web for many websites, it gained a particular pitch with the rise of the Web 2.0 era of computing, in which JavaScript became increasingly used for the development of user interfaces for applications, both web-based and desktop-based.

JavaScript was also combined with CSS to create dynamic web pages, which have also become popular as a more efficient and accessible alternative to Flash-based websites.

With the expanded demands for JavaScript, an easier means for programmers to develop such dynamic interfaces was needed. Thus, JavaScript libraries such as Prototype, script.aculo.us, Ext Core, JsPHP, MooTools and jQuery and JavaScript widget libraries such as Webix, Ext JS, DHTMLX, and Dojo Toolkit were developed, allowing for developers to concentrate more upon more distinctive applications of Ajax. This has led to other companies and groups, such as Microsoft and Yahoo! developing their own JavaScript-based user interface libraries, which find their way into the web applications developed by these companies.

...
Wikipedia