Observer patterns

The Observable pattern is one that allows an object, called subject, to keep track of other objects, called observers, interested in the subject state. When the subject state changes, it notifies its observers about it. The mechanics behind this are really simple.

TypeScript Observable

Let's take a look at the following Observer/Subject implementation in pure TypeScript (that is no Angular or framework of any kind, just TypeScript).

First, I defined an Observer interface that any concrete implementation will have to implement:

export interface Observer{ 
  
   notify(); 
} 

This interface only defines the notify() method. This method will be called by the subject (that is the Object being observed by...