Any need to call unsubscribe for RxJS first()

Question

In the following code:-

RxJS.Observable.of(1,2).first().subscribe((x) => console.log(x););

is it necessary to unsubscribe given the operator first()?

score 43 · Accepted Answer · edited Nov 10 '20 at 09:41

43

No. It unsubscribes automatically after calling first(). The current syntax is observable.pipe(first()).subscribe(func); for RxJS 6.

The documentation states:

If called with no arguments, first emits the first value of the source Observable, then completes.

edited Nov 10 '20 at 09:41

Max

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answered Nov 17 '18 at 02:38

Xavier Reyes Ochoa

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Think you are missing a `)` :) – El Ronnoco Jan 28 '19 at 11:57
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what happens when the source observable never emits a value, does that mean that the Subscription stays there and possibly create a memory leak ? – Gagan Sep 19 '19 at 16:05
@Gagan Yes, it can create a memory leak. – Max Nov 10 '20 at 08:18
So how to add unsubscribing in this case? – Tony Nov 23 '20 at 12:34

score 5 · Answer 2 · answered Apr 06 '18 at 02:23

5

For the example provided, you dont need to unsubscribe, and neither you need to call first, as Observable.of(1) actually completes after emitting its first (and last) value.

answered Apr 06 '18 at 02:23

c69

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Changed to 1,2 but your answer still is correct since you mentioned it Completes. – bhantol Apr 06 '18 at 11:49

Johan.C · Answer 3 · 2018-04-06T02:34:45.897

3

first() will complete after the first item is emitted from the observable.

Also subscribe() takes three arguments, the last one being the complete callback. Running the following code will output 1 followed by 'done'.

Rx.Observable.of(1)
  .subscribe(
  (x) => console.log(x),    // next
  (x) => console.error(x),  // error
  () => console.log('done') // done
)

edited Apr 06 '18 at 02:34

answered Apr 06 '18 at 01:54

Johan.C

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Any need to call unsubscribe for RxJS first()

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