Ext JS ships with more than 300 classes. So before going into further detail, let's understand basic class system of Ext JS 4, 5 and 6.
Ext is a global singleton class and also a top level namespace which you would use almost everywhere in Ext JS. Ext class has 78 methods and 59 properties. Some of the important methods that will be used frequently such as Ext.application(), Ext.apply(), Ext.create(), Ext.define(), Ext.getCmp(), Ext.override() etc.
All the classes namespace in Ext JS API starts from 'Ext'. Visit doc.sencha.com for more information on Ext class in Ext JS 6.x.
The following table lists some of the important classes in Ext JS API:
|Ext||The Ext namespace (global object) encapsulates all classes, singletons, and utility methods provided by Sencha libraries.|
|Ext.Base||The root of all classes created with Ext.define. Ext.Base is the building block of all Ext classes. All classes in Ext inherit from Ext.Base. All prototype and static members of this class are inherited by all other classes.|
|Ext.ClassManager||Ext.ClassManager manages all classes and handles mapping from string class name to actual class objects throughout the whole framework.|
|Ext.Loader||Ext.Loader is the heart of the new dynamic dependency loading capability in Ext JS 4+. It is most commonly used via the Ext.require shorthand.|
Visit Sencha doc for more information on Ext JS class system.