GarryBrown

  protected _next(value: T): void {
    this.destination.next(value);
  }

  protected _error(err: any): void {
    this.destination.error(err);
    this.unsubscribe();
  }

  protected _complete(): void {

GarryBrown

  unsubscribe(): void {
    if (this.closed) {
      return;
    }
    this.isStopped = true;
    super.unsubscribe();
  }

GarryBrown

class Observable<T> implements Subscribable<T> {...}

export interface Subscribable<T> {
  subscribe(observer?: PartialObserver<T>): Unsubscribable;
}

type PartialObserver<T> = NextObserver<T> | ErrorObserver<T> | CompletionObserver<T>;

GarryBrown

  class Observable<T> implements Subscribable<T> {
  ...
  
    constructor(subscribe?: (this: Observable<T>, subscriber: Subscriber<T>) => TeardownLogic) {
      if (subscribe) {
        this._subscribe = subscribe;
      }
    }
  }
  

GarryBrown

subscribe(observer?: PartialObserver<T>): Subscription;
subscribe(observerOrNext?: PartialObserver<T> | ((value: T) => void) | null,
            error?: ((error: any) => void) | null,
            complete?: (() => void) | null): Subscription {

    const sink = toSubscriber(observerOrNext, error, complete);

    sink.add(
      this._subscribe(sink) // call fn wicth we pass to constructor
    );

GarryBrown

class Customer {
  checkEmail(news) {
    // here we take a look on news and make a decision buy or not
  }

  findAnotherShop() {
    // search for a new shop for us
  }
  
  checkOrder() {