Pub/Sub, which means Publish-Subscribe, uses a more structured approach. Instead of depending on DOM components, it uses a central message bus, similar to an events message board. Here is the summary:

- Publishers: These are the event announcers who broadcast messages (events) via the messaging bus.
- Subscribers: These are the visitors who registered to receive specific announcements (events). When a relevant interaction comes, subscribers get notified and can take action.

The Composite pattern defines two basic types of elements sharing the same interface: simple leaves and complex containers. A container can consist of both leaves and other containers. This allows for the construction of a nested, recursive structure of objects resembling a tree.

Why Design Patterns are important

1. Scalability

Design Patterns help break your app into small, reusable pieces. This makes it easy to add new features later without messing up existing ones.

2. Maintainability

Following design patterns ensures your code has a clear, organized structure.

For example using patterns like the Singleton Pattern makes the app more maintainable because you only have to change one piece of code in the service, and all the components that depend on it will automatically adapt.

3. Testability

Design patterns promotes the separation of concerns which makes it easier to mock and test components

4. Code Reusability

Patterns encourage writing reusable code.

For example, patterns like Factory and Singleton help you organize similar tasks in one place, so you can easily reuse them without rewriting the same logic.