class MyObservable extends Rx.Observable {

  lift(operator) {

    const observable = new MyObservable();

    observable.source = this;

    observable.operator = operator;

    return observable;

  }

​

  customOperator() {

    return this.map(arguments)

  }

}

​

​

// instantiating an observable with **MyObservable**.from

var observable = MyObservable.from([1, 2, 3]);

console.log('instance of Rx.Observable: ' + observable instanceof Rx.Observable);

​

​

// this works as map is defined on RxObservable

observable

  .map(value => console.log('standard ' + value)) 

  .subscribe();

​

​

// this doesn't work. customOperator is only defined on MyObservable and MyObservable.from([1, 2, 3]) returns an Rx.Observable instance

observable

  .customOperator(value => console.log('custom ' + value)) 

  .subscribe();