Mastering JavaScript Promises

The publisher/subscriber

Events are yet another solution to communicate when asynchronous callbacks finish execution. An object can become emitter and publish events that other objects can listen to. This is one of the finest examples of the observer pattern.

The nature of this method is similar to "event listener", but much better than the latter because we can view the "message center" in order to find out how much signal is present and the number of subscribers for each signal, which runs the monitoring program.

A brief account of the observer pattern

The observer provides very loose coupling between objects. This provides the ability to broadcast changes to those who are listening to it. This broadcast may be for the single observer or a group ...