Coming from the promise land, I was never aware of how .finally was substituted when subscribed to an observable.

The easy way of how I was using was to add it on complete the third param of subscribe

BUT whenever an error occurs on the http request the subscribe never calls the complete method

You can find more info here and here

To use finally like we do when dealing with Promises, we can use finalize operator and pipe it through the observable$ like this

this.someService.fetchDataFromApi()
  .pipe(
    finalize(() => {
      this.isBusy = false;
    }).subscribe(()=>{
     // next
    }, () => {
     // error
    }, () => {
     // complete
    });

I did have a look of another easier method - to add a function at the end of subscription by using .add() but it is actually used to add a teardown method on the subscription or add more subscription/child to your existing subscription. So the better way would be to use finalize as illustrated on the code above.

If you find other ways then please do share it :)