Ext is a client-side, JavaScript framework for building web applications. In early 2006, Jack Slocum began working on a set of extension utilities for the Yahoo! User Interface (YUI) library under the name "yui-ext." In the fall of 2006, Jack released version .33 of yui-ext, which turned out to be the final version of the code under that name (and under the open source BSD license). By the end of the year, the library had gained so much in popularity that the name was changed simply to Ext, a reflection of its maturity and independence as a framework. A company was formed in early 2007, and Ext is now dual-licensed under the GPL v3 and a proprietary license.

Since Ext JS is developed behind closed doors, the repository for the code-analysis is just a static copy of the latest release.