Observable.fromArray.ts

import {Observable, Subscriber} from 'rxjs';

class RX {
	fromArray(array: Array<T>): Observable<Array<T>> {
		return Observable.create((subscriber: Subscriber<Array<T>>) => {
			try{
				array.forEach((value: T, index: number) => subscriber.next(value));
			}catch(e){
				subscriber.error(e);
			}

			subscriber.complete();
		});
	}
}

let rx = new RX();

rx.fromArray([1,2,3,4])
	.concatMap(item => Observable.of(item * 2).delay(500))
	.subscribe(value => console.log(value));