Hands-On Functional Programming with TypeScript

The observer pattern

In an implementation of the observer pattern, we can have many known listener entities that subscribe to messages. The following code snippet contains a very basic implementation of a listener in the observer pattern:

class Listener<T> {    public update: (message: T) => void;    public constructor(fn: (message: T) => void) {        this.update = fn;    }}

A Listener has a method named update, which is invoked when a second entity known as the Producer generates a new message. A Producer instance manages a number of Listener instances. A message can be generated with the notify method. The message is then passed to all the subscribed listeners. The following code snippet contains a very basic implementation of a producer in the observer ...