The art of debugging is as important as the art of programming. We usually write code that we think is going to work as soon as we execute it, but this is not true sometimes. We write the code, then we get an exception or JavaScript error, and then we need to dive into the code again to see where we went wrong. It's part of being a developer and it is also part of life!

Throughout this book, you learned that debugging is important, especially when we were learning an easier way to figure out the correct Component Query selector. When developing applications with Ext JS, it is mandatory to use a debug tool. This is so because it is not only for debugging, but you will also be able to learn more about the framework, and it is a great learning exercise.

A few things we always need to remind ourselves of while creating Ext JS applications: case-sensitive matters—the LoginScreen class is different from Loginscreen. Be careful with reserved words (http://mattsnider...