If you know JavaScript you must have realized the awesomeness of this programming language. The event model is one of the strongest pillar to make JavaScript so popular. The publisher-subscriber design(also known as observer pattern) takes this event model to one step further where clients can register them selfs to a event publisher. Any number of client can register themselves as subscriber. Publisher then notifies the subscriber for each message it published.When client do not want the subscribed message anymore it can unregister itself from the publisher. In total it provides freedom to both publisher and subscriber to define there own boundary and helped them to loosely coupled. in return helps a developer to implement separate the concerns of logic.
The reactive programming advances the observer pattern where a controlled Asynchronous data flow stream can be implemented.Reactive programming enables applications to make more real-time responsive.