Visibility.js allow you to determine whether your web page is visible to an user, is hidden in background tab or is prerendering. It allows you use the page visibility state in JavaScript logic and improve browser performance by disabling unnecessary timers and AJAX requests, or improve user interface experience (for example, by stopping video playback or slideshow when user switches to another browser tab).
Apple's official iOS UI guidelines. Will be pretty important going forward for iOS development, as this is some of the stuff that Apple looks for when approving Apps.
Metro JS is a JavaScript plugin for jQuery developed to easily enable Metro interfaces on the web. This release focuses on Live Tiles, the Application Bar and Theming. It's early in the development phase, but all features should work on at least IE7+(Win/WinPhone), Firefox, Chrome, Android, Opera, and Safari(OSX/iOS).
In the red corner, weighing in at just 29Kb (uncompressed), is knockout.js; a pure JavaScript library that simplifies the creation of dynamic user interfaces. Knockout is library agnostic, so it can easily be used with any of the most popular JavaScript libraries already available, but it works particularly well with jQuery, and uses jQuery.tmpl as its default templating engine.
This is an easy to understand article about the Promise pattern for Javascript. It is a way to have a 'continue with this function when this previous one succeeds' that doesn't involve nesting functions.
The jqXHR objects returned by $.ajax() as of jQuery 1.5 implement the Promise interface, giving them all the properties, methods, and behavior of a Promise.