Why is it easy to check .closed on manual RxJS subscriptions, but not with...

I am using RxJS for subscriptions in Angular. I noticed that when I manually subscribe to an observable and store the Subscription, I can easily check if it was unsubscribed using .closed, especially in ngOnDestroy().

But when I use the newer takeUntilDestroyed() utility (from @angular/core/rxjs-interop), I don’t get a Subscription object, so I can’t check if the unsubscription actually happened. This makes it harder to confirm at runtime whether the observable was cleaned up properly. Here’s current example of Old Subscription approach:

Manual Subscription (with .closed check):

import { Component, OnDestroy, OnInit } from '@angular/core';
import { interval, Subscription } from 'rxjs';
@Component({
selector: 'app-manual-sub',
template: `<p>Manual subscription</p>`
})
export class ManualSubComponent implements OnInit, OnDestroy {
subscription!: Subscription;
ngOnInit(): void {
this.subscription = interval(1000).subscribe(val => {
console.log('Manual:', val);
});
}
ngOnDestroy(): void {
this.subscription.unsubscribe();
console.log('Unsubscribed?', this.subscription.closed); // Easy to check
}
}


My Question:

Is there a way to confirm at runtime that takeUntilDestroyed() actually unsubscribed — similar to how we can check .closed on a Subscription? Is there a recommended pattern or function to track this more explicitly when using takeUntilDestroyed() ?

Thanks in advance

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