1. Principle being followed: Open-closed principle states that “objects or entities should be open for extension but closed for modification”. in our code, we tried to modify a class using “implement”. An example is from post.controller.ts where the PostController implements Icontroller. Rather than dynamically change the class of IController, implements allows ‘PostContoller’ inherit all the methods and properties from ‘IController’ , so we can modify the unique property in the new class.

2. Principla being followed: Dependency Inversion Principle It states “It states that the high-level module must not depend on the low-level module, but they should depend on abstractions.” In our code, the file authentication.service.mockup.ts, there is a MockAuthenticationService class which is a high level module and follows the open-close principle.

Also, in Authentication.controller.ts file, we have a “registration” method in AuthenticationController class. It is a low level module. In this class, we use a constructor function to provide a service. We wanted to make it dependent on abstractions, we use interface IAuthenticationService instead of using MockAuthenticationService.