YUI

YUI (Yahoo User Interface Library) is a deprecated JavaScript and CSS framework that was developed by Yahoo for building richly interactive web applications. It provided a comprehensive collection of utilities and controls including DOM manipulation, event handling, Ajax, animations, and UI widgets. YUI emphasized modularity with a sophisticated dependency management system that loaded only required components for optimal performance. The library included a powerful widget infrastructure for creating complex UI components like DataTables, Calendars, AutoComplete, and Rich Text Editors. YUI featured strong emphasis on accessibility, internationalization, and cross-browser compatibility with extensive documentation and examples. The project was officially retired in 2014 with Yahoo recommending migration to modern alternatives like React, Angular, or Vue. Websites still using YUI are running legacy code that should be modernized to current JavaScript frameworks and libraries.