Do I need to unsubscribe each time onDestroy in component?

Question

I am wondering If I subscribe to stream in my constructor like this:

_eventEmitterService.event.subscribe((msg)=>{})

So when I change the view to different component, and come back, the events are triggered twice from that stream. Do I need to unsubscribe each time I change the component, by using ngOnDestroy?

Thanks

Yes you do. I would have given you the link where it states that in the documentation, but I cannot find it any more — Poul Kruijt, Apr 22 '16 at 13:16
Check this answer about when to unsubscribe https://stackoverflow.com/a/51732897/3100587 — Mouneer, Aug 08 '18 at 09:52

score 13 · Accepted Answer · answered Apr 22 '16 at 13:19

I found it! And yes, per documentation as stated in the angular2 lifecycle-hook guide:

ngOnDestroy
Cleanup just before Angular destroys the directive/component. Unsubscribe observables and detach event handlers to avoid memory leaks.

So yes, you need to unsubscribe from observables on ngOnDestroy()

score 5 · Answer 2 · answered Apr 22 '16 at 13:48

5

Just an additional hint to the Pierre's great answer. The async pipe automatically unsubscribes observables it's applied on. So you need to unsubscribe for observables you manage by your own.

See this line in source code:

https://github.com/angular/angular/blob/master/modules/angular2/src/common/pipes/async_pipe.ts#L74

answered Apr 22 '16 at 13:48

Thierry Templier

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Github link is dead now. Could you expand a little bit more, your answer seems to contradict Pierre a bit, so I'm unsure when I need to manually cleanup? Angular official tutorial doesn't do any cleanups as far as I can see. – Davor Jun 29 '17 at 08:40

Do I need to unsubscribe each time onDestroy in component?

2 Answers2