Disclaimer

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#Introduction to Application Architecture

Ext JS provides support for both MVC and MVVM application architectures. Both of these 
architectural approaches share certain concepts and focus on dividing application code 
along logical lines. Each approach has its strengths based on how it chooses to divide 
up the pieces of an application.

The goal of this guide is to provide you with foundational knowledge regarding the 
components that make up these architectures. 

##What is MVC?

In an MVC architecture, most classes are either Models, Views or Controllers. 
The user interacts with Views, which display data held in a Model.  Those interactions are 
monitored by a Controller or the Model's business logic, which then responds to the 
interactions by updating the View and Model, as necessary. 

The View and the Model are generally unaware of each other because the Controller has the 
sole responsibility of directing updates. Views typically have little (if any) business 
logic, and Models are primarily an interface to data that allow for business logic 
regarding changes to said data.  Generally speaking, Controllers will contain most of 
the application logic within an MVC application.

One of the main advantages of an MVC architecture in web applications is that it helps to 
avoid enormous files full of spaghetti code. The goal of MVC is to clearly define the 
responsibilities of each piece of the application. Because every class (i.e. every file) 
has clearly defined responsibilities, they implicitly become ignorant of the larger 
environment – making the app easier to test, easier to maintain, and allowing 
code to be reused.

##What is MVVM?
The key difference between MVC and MVVM is that MVVM features an abstraction of a View 
(the ViewModel), which manages the changes between a Model’s data and the View's 
representation of that data (i.e. data bindings) – something that can be 
cumbersome to manage in traditional MVC applications.

The result is that the Model and framework perform as much work as possible, minimizing 
or eliminating application logic that directly manipulates the View.

##Returning Users

Ext JS 5 introduces a new MVVM architecture as well as a new take on the (C) in MVC.    
That said, it is important to note that the classic Ext JS 4 MVC implementation will 
continue working in the same manner.  We DO encourage you to take advantage of our exciting 
new functionality, but you shouldn't feel obligated to restructure your application.

**Note:** Sencha Cmd's starter app, produced by `sencha generate app`, currently produces 
an MVVM structure.  However, you can simply delete the default viewModel to continue 
building your application as before.