docs: clarify expectations for `ActivatedRoute` observables (#42316)
https://github.com/angular/angular/issues/16261#issuecomment-748289240 A couple important things to note about the behavior: * The component is destroyed, meaning that all of its members will be destroyed as well, including any subscriptions to the route params * This _does not_ mean that any `finalize` operators or `complete` on the subscription is called. This only happens if the source completes or you unsubscribe from the subscription. The documentation doesn't state that the `Router` will do this, though I can still understand why the behavior is confusing. You can play around with these scenarios here: https://stackblitz.com/edit/rxjs-hmpizx * `complete` the source without unsubscribe: `next`, `complete` and `finalize` are all called, even when `complete` is called before the `next` from the `delay` * `unsubscribe` from subscription without `complete` on the source: `finalize` happens, but the `complete` of the subscription does not, and neither does `next` So even if the `Router` were to call `complete` on all of the `Observables` on an `ActivatedRoute`, you would see that any subscriptions with a `delay` operator would still get called. resolves #16261 PR Close #42316
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@ -1002,7 +1002,12 @@ Since `ngOnInit()` is only called once per component instantiation, you can dete
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When subscribing to an observable in a component, you almost always unsubscribe when the component is destroyed.
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However, `ActivatedRoute` observables are among the exceptions because `ActivatedRoute` and its observables are insulated from the `Router` itself.
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The `Router` destroys a routed component when it is no longer needed along with the injected `ActivatedRoute`.
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The `Router` destroys a routed component when it is no longer needed. This means all the component's members will also be destroyed,
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including the injected `ActivatedRoute` and the subscriptions to its `Observable` properties.
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The `Router` does not `complete` any `Observable` of the `ActivatedRoute` so any `finalize` or `complete` blocks will not run.
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If you need to handle something in a `finalize`, you will still need to unsubscribe in `ngOnDestroy`. You will also have to
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unsubscribe if your observable pipe has a delay with code you do not want to run after the component is destroyed.
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