How to force call `super.ngOnDestroy`

Question

I have an abstract class that helps in avoiding repetitive code (to unsubscribe observables), it looks like:

export abstract class SubscriptionManagmentDirective implements OnDestroy {
  componetDestroyed = new Subject<void>()

  constructor() {}

  ngOnDestroy(): void {
    this.componetDestroyed.next()
    this.componetDestroyed.unsubscribe()
  }
}

In some cases it happened that I override ngOnDestroy and forget to call super.ngOnDestroy() and then subscriptions go wild. I added a unit test to the extending components to test that un-subscriptions has been called, but to do so I have to actually remember to add them.

My question is,

• is there a way to force that super.ngOnDestroy() is called whenever the component is extended?
• or is there a way to write a unit test for the abstract class that would be tested on any component that extend that class?

Any help would be appreciated, thanks.

Answer 1

1. No, there is no such way to auto call method from an abstract.

2. You have to unit test only in isolation. Just create an inline test class that extends your abstract and then unit test ngOnDestroy. It's totally enough.

Answer 2

I can think of only one way, very hacky and ugly. One thing that is enforced is the super() call in the constructor, by TypeScript itself. Therefore you could

class Foo {
  constructor() {
    const oldNgOnDestroy = this.ngOnDestroy;

    this.ngOnDestroy = function() {
      console.log("decorated ngOnDestroy");
      return oldNgOnDestroy();
    }.bind(this);
  }

  ngOnDestroy() {
    console.log("original ngOnDestroy");
  }
}

class Bar extends Foo {
  constructor() {
    super();
  }
}

class Baz extends Foo {
  constructor() {
    super();
  }

  ngOnDestroy() {
    console.log("custom ngOnDestroy");
  }
}

const bar = new Bar();
bar.ngOnDestroy();
const baz = new Baz();
baz.ngOnDestroy();

As I said, hacky and ugly.