JSConcepts

Observer vs Pub-Sub pattern

Observer

The observer pattern is a software design pattern in which an object, called the subject, maintains a list of its dependents, called observers, and notifies them automatically of any state changes, usually by calling one of their methods.

Pub-Sub

In ‘Publisher-Subscriber’ pattern, senders of messages, called publishers, do not program the messages to be sent directly to specific receivers, called subscribers.

Difference

• In the Observer pattern, the Observers are aware of the Subject, also the Subject maintains a record of the Observers. Whereas, in Publisher/Subscriber, publishers and subscribers don’t need to know each other. They simply communicate with the help of message queues or broker.
• In Publisher/Subscriber pattern, components are loosely coupled as opposed to Observer pattern.
• Observer pattern is mostly implemented in a synchronous way, i.e. the Subject calls the appropriate method of all its observers when some event occurs. The Publisher/Subscriber pattern is mostly implemented in an asynchronous way (using message queue).
• Observer pattern needs to be implemented in a single application address space. On the other hand, the Publisher/Subscriber pattern is more of a cross-application pattern.

Reference

https://hackernoon.com/observer-vs-pub-sub-pattern-50d3b27f838c