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.