Thank you for your response! We really appreciate your opinion!

We meant that one developer who knows Javascript could build common apps.

Of course, you are right! If you want to create a complex app you need to learn additional technologies. It’s like everywhere! For example, there are different approaches to make an espresso and a latte with a coffee machine. To make a latte first you need to learn how to make an espresso. As it is basics. Then you need to learn how to make a milk foam, etc.

The more complex your app needs to be, the more technologies you need to use to build it.