ExtJS 4.x was based on MVC (Model-View-Controller) architecture. Ext JS supports MVVM (Model-View-ViewModel) architecture since Ext JS 5.
In the MVVM architecture, the job of Model and View remains the same as MVC.
Model is a collection of data fields which persist through the data package. They can be linked to other models through associations and linked to a data stream through the use of a proxy.
View is any type of components that output information on to your browser, i.e. Container, Form, Grid, Chart.
ViewModel is a class that manages data for the specific view.
ViewController: Ext JS 5 introduced ViewController which will be attached to a specific view and will handle all the events of that view.