simple observer for rxjs

import { Observable } from 'rxjs';
/* import { Observable } from 'rxjs/Observable';
import  'rxjs/add/operator/map';
import  'rxjs/add/operator/filter'; */

let numbers = [1, 5, 10];

let source = Observable.create(observer => {
    let index = 0;
    let produceValue = () => {
        observer.next(numbers[index++]);

        if (index < numbers.length) {
            setTimeout(produceValue(), 250);
        } else {
            observer.complete();
        }
    }

    produceValue();
}).map(n => n * 2)
.filter(n => n > 4);

source.subscribe(
    value => console.log(`value: ${value}`),
    e => console.log(`error: ${e}`),
    () => console.log(`complete`)
);

/* class MyObserver implements Observer<number> {
    next(value) {
        console.log(`value: ${value}`);
    }

    error(e) {
        console.log(`error: ${e}`);
    }

    complete() {
        console.log(`complete`);
    }
} */