AngularJS is built around the belief that declarative programming should be used for building user interfaces and wiring software components, while imperative programming is excellent for expressing business logic. The framework adapts and extends traditional HTML to better serve dynamic content through two-way data-binding that allows for the automatic synchronization of models and views. As a result, AngularJS de-emphasizes DOM manipulation and improves testability & performance.
Decouple DOM manipulation from application logic. This improves the testability of the code.
Regard application testing as equal in importance to application writing. Testing difficulty is dramatically affected by the way the code is structured.
Decouple the client side of an application from the server side. This allows development work to progress in parallel, and allows for reuse of both sides.
Provide structure for the journey of building an application: from designing the UI, through writing the business logic, to testing.
Angular follows the MVC pattern of software engineering and encourages loose coupling between presentation, data, and logic components. Using dependency injection, Angular brings traditional server-side services, such as view-dependent controllers, to client-side web applications. Consequently, much of the burden on the backend is reduced, leading to much lighter web applications.
AngularJS directives allow the developer to specify custom and reusable HTML tags that moderate the behavior of certain elements.
Declares an element as a root element of the application allowing behaviors to be modified through custom HTML tags.
Changes the text of an element to the value of an expression.<spanng-bind="name"></span> will display the value of ‘name’ inside the span. Any changes to ‘name’ are reflected instantly in the DOM anywhere the variable is used.
Similar to ng-bind, but allows two-way data binding between the view and the scope.
Allows tuning how model updates are done.
Allows class attributes to be dynamically loaded.
Instantiate an element once per item from a collection.
ng-show & ng-hide
Conditionally show or hide an element, depending on the value of a boolean expression. Show and hide is achieved by setting the CSS display style.
Conditionally instantiate one template from a set of choices, depending on the value of a selection expression.
The base directive responsible for handling routes that resolve JSON before rendering templates driven by specified controllers.
Basic if statement directive which allow to show the following element if the conditions are true. When the condition is false, the element is removed from the DOM. When true, a clone of the compiled element is re-inserted
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. 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.
In July 2012, the Angular team built a plugin for the Google Chrome browser called Batarang, that improves the debugging experience for web applications built with Angular. The extension aims to allow for easy detection of performance bottlenecks and offers a GUI for debugging applications. The extension is not compatible with recent releases of Angular.
AngularJS was originally developed in 2009 by Miško Hevery and Adam Abrons  at Brat Tech LLC as the software behind an online JSON storage service, that would have been priced by the megabyte, for easy-to-make applications for the enterprise. This venture was located at the web domain "GetAngular.com", and had a few subscribers, before the two decided to abandon the business idea and release Angular as an open-source library.
Abrons left the project, but Hevery, who works at Google, continues to develop and maintain the library with fellow Google employees Igor Minár and Vojta Jína.
The most prominent feature that separates the two libraries is in the way models and views are synchronized. Whereas AngularJS supports two way data-binding, Backbone.js relies heavily on boilerplate code to harmonize its models and views.
Backbone.js communicates well with RESTful backends. A very simple use of REST APIs is also available with AngularJS using the $resource service. AngularJS also provides a $http service which is more flexible, connecting to remote servers either through a browser's XMLHttpRequest object or via JSONP.
AngularJS templating uses a combination of customizable HTML tags and expressions. Backbone.js ships with underscore.js's utility function template() and also integrates with different templating engines such as Mustache.