Knockout is a JavaScript library that helps you to create rich, responsive display and editor user interfaces with a clean underlying data model. Any time you have sections of UI that update dynamically (e.g., changing depending on the user?s actions or when an external data source changes), KO can help you implement it more simply and maintainably.

Knockout is very well documented and comes up with a full list of examples so learning how to use it is very simple.

Some of the key features are:

• Elegant dependency tracking – automatically updates the right parts of your UI whenever your data model changes
• Declarative bindings – a simple and obvious way to connect parts of your UI to your data model
• Flexible and sophisticated templating – construct a complex dynamic UI easily using arbitrarily nested templates
• Trivially extensible – implement custom behaviors as new declarative bindings for easy reuse in just a few lines of code

Also this library is compact as it has only 25kb before zipping.