AngularJS Fundamentals

AngularJS is an open-source JavaScript framework, maintained by Google, that assists with running single-page applications. Its goal is to augment web-based applications with model–view–controller (MVC) capability, in an effort to make both development and testing easier.
The library reads in HTML that contains additional custom tag attributes; it then obeys the directives in those custom attributes, and binds input or output parts of the page to a model represented by standard JavaScript variables. The values of those JavaScript variables can be manually set, or retrieved from static or dynamic JSON resources.

Most Important feature is 

Two-way data binding

AngularJS' two-way data binding is its most notable feature and reduces the amount of code written by relieving the server backend from templating responsibilities. Instead, templates are rendered in plain HTML according to data contained in a scope defined in the model. The $scope service in Angular detects changes to the model section and modifies HTML expressions in the view via a controller. Likewise, any alterations to the view are reflected in the model. This circumvents the need to actively manipulate the DOM and encourages bootstrapping and rapid prototyping of web applications.[3] AngularJS detects changes in models by comparing the values with stored earlier values in a process of dirty-checking, unlike Ember.js and Backbone.js which trigger listeners when the model values are changed