Difference between Observables and Promises in Angular

Chittaranjan Swain

7y1.3kAngular

Hi all,

What is the Difference between Observables and Promises in Angular 2 or higher version.

5 Replies

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7y ago
Accepted answer
Promise

A Promise handles a single event when an async operation completes or fails.There are Promise libraries out there that support cancellation, but ES6 Promise doesn't so far.

Observable

An Observable is like a Stream (in many languages) and allows to pass zero or more events where the callback is called for each event.

Often Observable is preferred over Promise because it provides the features of Promise and more. With Observable it doesn't matter if you want to handle 0, 1, or multiple events. You can utilize the same API in each case.

Observable also has the advantage over Promise to be cancelable. If the result of an HTTP request to a server or some other expensive async operation isn't needed anymore, the Subscription of an Observable allows to cancel the subscription, while a Promise will eventually call the success or failed callback even when you don't need the notification or the result it provides anymore.

Observable provides operators like map, forEach, reduce, ... similar to an array

There are also powerful operators like retry(), or replay(), ... that are often quite handy.
Mohanraj Kaliappan7y ago
Please go through the below URL.
https://stackoverflow.com/questions/37364973/what-is-the-difference-between-promises-and-observables/51798551#51798551
Amit Mohanty7y ago
Both Promises and Observables will help us work with the asynchronous functionalities. They are very similar in many cases, however, there are still some differences between the two as well, promises are values that will resolve in asynchronous ways like http calls. On the other hand, observables deal with a sequence of asynchronous events. The main differences between them are listed below:

promise:

having one pipeline
usually only use with async data return
not easy to cancel

observable:

are cancellable
are retriable by nature such as retry and retryWhen
stream data in multiple pipelines
having array-like operations like map, filter etc
can be created from other sources like events
they are functions, which could be subscribed later on
Vikas7y ago
Promise:-
In simple word Promises work asynchronous and return a single value or error message.
Another important thing to remember about promises is that you can not undo the initiated request.
Observables:-
Observables provide support for passing messages between publishers and subscribers in your application.
Observables offer significant benefits over other techniques for event handling, asynchronous programming, and handling multiple values.
Supports collection operators like map, filters.
Following features available ES 2016.
Always can be canceled.
Using RX JS.
Rajanikant Hawaldar7y ago
go through below video, difference between observables and promises in angular 2 https://youtu.be/JFx3amVu1Yg