JQuery UI
jQuery UI was a MediaWiki user interface framework in use in the 2000s. It was the third party library jQuery UI, but with some modifications. It was deprecated in favor of more modern frameworks.
History
[edit]jQuery was introduced in 2009 and with MW 1.16, jquery.ui was added around the same time as the Vector skin in order to provide a new and improved editing interface. It started with dialog component for the 2010 wikitext editor. While it was not announced as a standard user-interface library, it became part of several extensions in connection to the 2010 wikitext editor, such as CodeMirror and CodeEditor. Wikidata was intentionally built with jquery.ui due to a lack of standardization. Its simplicity also became popular with gadget authors. The 2010 wikitext editor and PageTriage are still widely-used extensions. jQuery.ui was deprecated in MW 1.29 for OOUI.
Development until this time was mainly driven by technical and feature-specific needs. Design standards were not enforced Foundation-wide. That is the background of yet another framework, Backbone, being chosen for PageTriage back then.