observables vs promises

Observables vs Promises

• A coworker of mine today asked me this splendid question and I thought it is worth to write down.

• A Promise handles only a single asynchronous event. When the asynchronous event is completed (success or fail), a callback is invoked.

• An Observable is based off of the Observer Pattern, which is when observers subscribe to a subject and are notified when the subject changes state so that they can react accordingly.
• More specifically, there can be zero to many observables that subscribe to an event, and when that event completes, (successfully or not) a callback is invoked for every event.
• Basically it is a function that takes an observer, which defines the next, complete, or error callbacks. The observable invokes the callbacks based on whether the event is a succession, a completion, or an error.

Conclusion:

An observable is much more powerful than a promise becuase it can handle more streams of events and data over a period of time, whereas a promise can only handle one asynchronous event.