I had an opportunity to work also with non-Ext frameworks while I was integrating wonderful Bryntum Scheduler and Gantt to Angular, React and while doing so I had to learn about the other frameworks. I already have a lot of experiences with ExtJS and I have written many large production-grade applications in this framework.
The correctly implemented ViewModel hierarchy in Ext 5.x MVVM applications provides for more robust, modularized and well-written large applications. Read this article to write big, yet maintainable, expandable and bugless applications.
Are you planning to upgrade your application to newer version of ExtJS? Read this article to see how to start with UI analysis and what to write to the Design Document.
Do you plan a new application or an upgrade of existing one? Read about the design phase of the project and learn what you must and must not do.
Have you ever been interested how many files your application consists of? Or how many lines have you and your developers have written in this app? Read to find how to easily count them.
How do we use asynchronous Ext.Msg to confirm Ext window close? Find out.
Theming in Ext does not need to be a difficult lot of work. It is very easy to implement color variations of an Ext theme, and that is sufficient for many projects anyway.
There was one piece of information missing in the source of this example: the grid columns configuration. I have added it in the comment, see it there.
You should not read this post. It describes a bad practice.
Although Sencha Cmd is a very useful tool for application scaffolding, creating view, controllers and models, sometimes it is faster to use a single-file app. It is especially useful for fast testing, prototyping or concept proof. Read how to do it.