Observable versus promise

This article contrasts observables (see Observer pattern) with promises (see Futures and promises).

Run conditions

• Observables are lazy -- they do not run unless subscribed to
• Promises run no matter what

Setup and teardown

• Observables can define both setup and teardown aspects of asynchronous behavior.

Cancellable

• Observables are cancellable.

Retriability

• Observables can be retried
• To retry promises, a caller must have access to the original function that returned the promise.

See also

• Futures and promises
• Observer pattern
• Promise object (JavaScript)