How to call a method of an observable in angular?

Question

I'm trying to call a business method after subscribe to an observable with rxjs but I cannot make it work. What I'm missing?

observable$.subscribe(value: A => {
  value.businessMethod();
});

class A {

  public businessMethod(): number {
    ...
  }
}

ERROR TypeError: "value.businessMethod is not a function"

Answer 1

I guess the error occurs when obervable$ does not hold a value yet. Its value is undefined. Please try

observable$.pipe(
  filter(Boolean),
).subscribe(value: A => {
  value.businessMethod();
});