Answer

• Bind the Data using expression {{}}. 
  
• Control DOM structures for repeating, showing and hiding DOM fragments. 
  
• Support for forms and form validation. 
  
• Attaching new behavior to DOM elements, such as DOM event handling. 
  
• Grouping of HTML into reusable components.
  

Answer

1. Registering callbacks: Registering callbacks is no more needed. 
   
2. Manipulating HTML DOM programmatically: AngularJS automatically synchronize the UI change when application state changes and vice versa, Therefore no need for DOM manipulation tasks. Although you can still do that if you want to. 
   
3. Marshaling data to and from the UI: The flow of data between the server and HTML form now handle by the AngularJS that eliminates almost all of the code required for posting and reading data using ajax calls. 
   
4. Writing tons of initialization code just to get started: With Angular you can bootstrap your app easily using services, which are auto-injected into your application in a Guice-like dependency-injection style. 
   

Answer
For easy manipulation of view with model and model with view, Google developed this MVVM JavaScript based framework usually for Single Page Application (SPA) projects. It extends the HTML document object model with extra attributes and makes it more responsive to user. Its is open source, completely free, developed and maintained by Google.