What is the difference between observer and subscriber?

An RxJS Subject is a special type of Observable that allows values to be multicasted to many Observers. While plain Observables are unicast (each subscribed Observer owns an independent execution of the Observable), Subjects are multicast. A Subject is like an Observable, but can multicast to many Observers.

Observables provide support for passing messages between parts of your application . They are used frequently in Angular and are a technique for event handling, asynchronous programming, and handling multiple values.

Observable are just that — things you wish to observe and take action on. Angular uses the Observer pattern which simply means — Observable objects are registered, and other objects observe (in Angular using the subscribe method) them and take action when the observable object is acted on in some way .

In the observer pattern, the observers are aware of the Subject . 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 a broker.

Observer : Any object that wishes to be notified when the state of another object changes. Observable : Any object whose state may be of interest, and in whom another object may register an interest.

Ideally, RxJS combines the Observer pattern with the Iterator pattern and functional programming with collections to fill the ideal way of managing sequences of events. So, it is not wrong to say that Observables in RxJS are a merger of observer and iterator software patterns .

An Observer is a consumer of values delivered by an Observable . Observers are simply a set of callbacks, one for each type of notification delivered by the Observable: next , error , and complete . The following is an example of a typical Observer object: const observer = { next: x => console.