In this chapter, you're going to learn about the class system, which was first introduced in Ext JS version 4. You are also going to learn how to load classes dynamically and how to interact with the Document Object Model (DOM) to modify the structure of the DOM tree for our convenience.

You should know that JavaScript is classless (prototype-oriented); however, we can emulate it using the prototype object and other techniques. One of the major features of Ext JS is that since version 4, all the code in the framework was developed with a class-based structure. Along with naming conventions, it's easy to learn and understand, and keep the code organized, structured, and easy to maintain.

Knowing and understanding the concept of the Object-Oriented Programming System (OOPS) is very important. This book may not be a focused guide on the concept of OOPS, but you are going to learn how we can use and implement this concept in Ext JS.

The following are the main topics...