Backbone.js supplies structure to JavaScript-heavy applications by providing models with key-value binding and custom events, collections with a rich API of enumerable functions, views with declarative event handling, and connects it all to your existing application over a RESTful JSON interface. Backbone.js was originally extracted from the Rails application DocumentCloud. Philosophically, Backbone is an attempt to discover the minimal set of data-structuring (models and collections) and user interface (views and URLs) primitives that are generally useful when building web applications with JavaScript. Backbone is a library, not a framework. Synchronous events are used as the fundamental building block over constantly polling data. The main pars of Backbone are: