https://observable-playground.github.io/gist/8c511ab73262d577254d5468f7f6fcd7

rxjs-playground-start.js

const { rxObserver } = require('api/v0.3');
const { Observable, ConnectableObservable, GroupedObservable, observable, Subject, BehaviorSubject, ReplaySubject, AsyncSubject, asapScheduler, asyncScheduler, queueScheduler, animationFrameScheduler, VirtualTimeScheduler, VirtualAction, Scheduler, Subscription, Subscriber, pipe, noop, identity, isObservable, ArgumentOutOfRangeError, EmptyError, ObjectUnsubscribedError, UnsubscriptionError, TimeoutError, bindCallback, bindNodeCallback, defer, empty, forkJoin, from, fromEvent, fromEventPattern, generate, iif, interval, never, of, pairs, range, throwError, timer, using, EMPTY, NEVER, config } = require('rxjs');
const { audit, auditTime, buffer, bufferCount, bufferTime, bufferToggle, bufferWhen, catchError, combineAll, combineLatest, concat, concatAll, concatMap, concatMapTo, count, debounce, debounceTime, defaultIfEmpty, delay, delayWhen, dematerialize, distinct, distinctUntilChanged, distinctUntilKeyChanged, elementAt, endWith, every, exhaust, exhaustMap, expand, filter, finalize, find, findIndex, first, groupBy, ignoreElements, isEmpty, last, map, mapTo, materialize, max, merge, mergeAll, mergeMap, flatMap, mergeMapTo, mergeScan, min, multicast, observeOn, onErrorResumeNext, pairwise, partition, pluck, publish, publishBehavior, publishLast, publishReplay, race, reduce, repeat, repeatWhen, retry, retryWhen, refCount, sample, sampleTime, scan, sequenceEqual, share, shareReplay, single, skip, skipLast, skipUntil, skipWhile, startWith, subscribeOn, switchAll, switchMap, switchMapTo, take, takeLast, takeUntil, takeWhile, tap, throttle, throttleTime, throwIfEmpty, timeInterval, timeout, timeoutWith, timestamp, toArray, windowCount, windowTime, windowToggle, windowWhen, withLatestFrom, zip, zipAll } = require('rxjs/operators');

// console.log(new Set(Object.keys(require('rxjs')))); 
// console.log(new Set(Object.keys(require('rxjs/operators')))); 

const msg = 'awesome';

timer(0, 5)
  .pipe(
    take(msg.length),
    map(index=>msg[index])
  )
  .subscribe(rxObserver());