Promises and Observables

Question

I am a beginner in angular 2 . In HTTP methods we are using Subject(BehaviourSubject) in our project and I know that Subject is a special kind of Observables and there are some unique features in that.

According to my knowledge,

Promises and Observables are used to get data from the API
We have to subscribe both promises or observables to get latest values

I cant get these things,

what is mean by cancellable and non-cancellable here?
Promises return single values while Observables return multiple values?

Anyone please explain me these things to understand better. Thanks in advance

Possible duplicate of [Angular - Promise vs Observable](https://stackoverflow.com/questions/37364973/angular-promise-vs-observable) — mxr7350, Aug 30 '17 at 10:15
I cant get cancellable there.. how can we cancel the subscription? — Praveen Eswaramoorthy, Aug 30 '17 at 10:24

score 0 · Accepted Answer · answered Aug 30 '17 at 10:28

0

Promises return single values while Observables return multiple values

Promises give you a promise that a value will be returned. Observables offer a streaming mechanism and may raise multiple events/return multiple values for a single subscription.

what is mean by cancellable and non-cancellable here?

The observable subscription can be (and should be) cancelled once no longer needed. It kind of makes sense if you think that they can return values "forever". Promises do not support cancellations (I think it was in the spec but finally was not implemented)

Hope this helps

answered Aug 30 '17 at 10:28

gpanagopoulos

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Thanks a lot. But how can we cancel the subscription of observables.. Do you mean that we have to remove the code where observables subscribe? – Praveen Eswaramoorthy Aug 30 '17 at 10:57
the subscribe() method returns a subscription obj. Then it is as simple as yourSubscription.unsubscribe(); – gpanagopoulos Aug 30 '17 at 11:04

Promises and Observables

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