AngularJS is a web application framework that makes creating complicated web applications much simpler. One of its best features is the ability to create directives, or reusable web components. It gives you the ability to create new HTML tags and attributes, which can dynamically display content in response to data changes, as well as update the data when appropriate.

Dependency injection in AngularJS is supremely useful, and the key to making easily testable components. This article explains how AngularJS dependency injection system works.