The NgModule — a class decorated with @NgModule
Decorator — is a fundamental feature of Angular.
JavaScript also has its own module system for managing collections of JavaScript objects. It's completely different and unrelated to the NgModule system.
In JavaScript each file is a module and all objects defined in the file belong to that module. The module declares some objects to be public by marking them with the export
key word. Other JavaScript modules use import statements to access public objects from other modules.