Observer patter writed into one typescript file
Observer is a behavioral design pattern that lets you define a subscription mechanism to notify multiple objects about any events that happen to the object they’re observing.
The Observer pattern suggests that you add a subscription mechanism to the publisher class so individual objects can subscribe to or unsubscribe from a stream of events coming from that publisher. Fear not! Everything isn’t as complicated as it sounds. In reality, this mechanism consists of 1) an array field for storing a list of references to subscriber objects and several public methods which allow adding subscribers to and removing them from that list.