In September 2009, Yahoo! released YUI 3, a new version of YUI 2. Among the enhancements are a CSS selector driven engine, like jQuery , for retrieving DOM elements, a greater emphasis on granularity of modules, a smaller seed file, and a variety of methods for making data faster and easier. 
The YUI Library project at Yahoo! was founded by Thomas Sha and sponsored internally by Yahoo! co-founder Jerry Yang ; Its main architects have been Sha, Adam Moore, and Matt Sweeney. The library’s developers maintain the YUIBlog; the YUI community discusses the library and implementations in its community forum.
The YUI Library is fully documented on its website; detailed API documentation accompanies the library download. It has six types of components: YUI core, utilities, UI controls, CSS components, developer tools, and build tools.
The YUI Core is a light (31KB minified) set of tools for event management and DOM manipulation.
- YUI Global Object
- The YUI Global Object contains language utilities, a script loader, and other baseline infrastructure for YUI.
- Dom Collection
- Helps with common DOM scripting tasks, Including element positioning and CSS management style.
- Event Utility
- Provides developers with easy and safe access to browser events (such as mouse clicks and key presses). It also provides the Custom Event object for publishing and subscribing to custom events.
- Helps create “effects” by animating the position, size, opacity or other characteristics of page elements.
- Browser History Manager
- Helps web applications use the browser’s back button and bookmarking functionality.
- Connection Manager
- Helps manage XMLHttpRequest transactions in a cross-browser fashion. It has integrated support for form posts, error handling , callbacks and file uploading.
- Allows you to manage cookies and subcookies through a simple API.
- Drag and drop
- The YUI Drag and Drop Utility makes it easy to make elements ” draggable ” and to create drop targets that respond to drag events.
- Provides a wrapper for HTML elements in the DOM and makes it simpler to use the same functions as adding listeners, manipulating the DOM, and setting and getting attributes.
- CSS files. The Get Utility supports the data loading.
- YUI’s ImageLoader makes it easy for you to load up the images that are not visible in the viewport. This can result in big performance boosts.
- Allows you to make any block-level HTML element resizable.
- The YUI Selector Utility allows you to grab references to HTML elements via CSS3 selector syntax.
- YUI Loader
- YUI Loader is a client-side loader that can dynamically load any YUI component (and dependencies) on the fly.
- Provides autocomplete feature (suggestion lists and type-ahead functionality) for user interactions involving text-entry. It supports a variety of data-source formats. It also supports server-side data-sources via XMLHttpRequest.
- Enables the creation of rich, graphical buttons that function like traditional HTML form buttons.
- A graphical, dynamic control used for date selection.
- The Charts Control retrieves data via the DataSource Utility and displays the data in a variety of common formats (line, bar, pie, etc.).
- Color Picker
- The Color Picker Control provides a rich visual interface for color selection.
- Supports a variety of DHTML windowing patterns including Tooltip , Panel, Dialog, SimpleDialog, Module and Overlay.
- Simple yet powerful API to display accessible screen-reader tabular data on a web page. Notable features include sortable columns, pagination, scrolling, row selection, resizable columns, and inline editing.
- ImageCropper provides the UI and interactive elements for a client-side image cropper.
- Layout Manager
- Allows you to create cross-browser, pixel perfect layouts with little effort by providing a fixed layout containing, top, bottom, left, right and center layout units.
- Provides an easy API for creating fly-out menus , menu bars, and context menus.
- Rich Text Editor
- The YUI Rich Text Editor is a sophisticated client-side text-processor that is modular and highly configurable, suitable for any open-ended text-entry situation.
- Provides a generic slider element that allows the user to choose from a range of values on one or two axes.
- Provides navigable tabbed views of content; supports dynamic loading of tab content via XMLHttpRequest.
- Produces a content tree whose nodes can be expanded and contracted.
- Allows for multi-file upload with feedback on upload progress.
- CSS Base
- Cross-browser replacement for the standard browser CSS rules to which web developers are accustomed.
- CSS Grids
- Seven basic page wireframes with subsection components to support over 1000 different page layouts.
- CSS Fonts
- Standardized cross-browser makes families and size rendering.
- CSS Reset
- CSS statements remove margins and standardize cross-browser rendering on common elements.
- Used in combination with Profiling to provide rich visualizations of your data profiling – both graphically (using the Charts Control) and in tabular format (using DataTable).
- YUI Test
- YUI Compressor
- CSS framework
- ^ Jump up to:a b “The Yahoo! User Interface Library ‘ . Yahoo! User Interface Blog . February 13, 2006.
- Jump up^ “YUI 3.17.2 Released” . http://www.yuiblog.com . Retrieved 14 September 2014 . External link in( help )
- Jump up^ “YUI Library” . Retrieved 13 June 2008 .
- Jump up^ “YUI 3.0.0: First GA Release of YUI’s Next-Generation Codeline” . Yahoo! User Interface Blog . September 29, 2009 . Retrieved 18 November 2009 .
- Jump up^ “Important Announcement Regarding YUI” . Yahoo! Engineering . Retrieved 29 August 2014 .