KnockoutJS is a very lightweight library (just 20 KB minified) that gives the ability to objects to become the nexus between views and models. It means that you can create rich interfaces with a clean underlying data model.
For this purpose, it uses declarative bindings to easily associate DOM elements with model data. This link between data and presentation layer (HTML) allows the DOM to refresh displayed values automatically.
Knockout set up chains of relationships between model data to transform and combine it implicitly. Knockout is also trivially extensible. It is possible to implement custom behaviors as new declarative bindings. This allows the programmer to reuse them in a just few lines of code.
The advantages of using KnockoutJS are many:
It's free and open source.
It is built using pure JavaScript.
It can work together with other frameworks.
It has no dependencies.
It supports all mainstream browsers, even ancient ones such as IE 6+, Firefox 3.5+, Chrome, Opera, and Safari (desktop/mobile).
It is fully documented with API docs, live examples, and interactive tutorials.
Knockout's function is specific: to join views and models. It doesn't manage DOM or handle AJAX requests. For these purposes, I would recommend jQuery. Knockout gives us the freedom to develop our code the way we want.
MVVM-pattern diagram