Ext JS is based on MVC/ MVVM architecture. The latest version of Ext JS 6 is a single platform which can be used for both desktop and mobile application without having different code for different platform.
With Ext JS 6, Sencha introduces a single framework for creating applications that run across all types of devices, from phones to tablets to desktops. You will be able to produce an optimal user experience while writing less code. Combined with a compelling new theme, Ext JS 6 has everything you need to create amazing experiences on any device.