Chaining promise in a loop to convert to an Observable

async-loop.js

// Allows an asynchronous loop to be converted to an Observable.
function loop(): Observable<number> {
  const subject = new DefaultSubject<number>();
  let promise = Promise.resolve();
  for (let i = 0; i < 3; i++) {
    promise = promise.then(async () =>
      await new Promise(resolve => {
        setTimeout(() => {
          subject.next(i);
          resolve();
        }, 1000);
      })
    )
  }

  promise
    .then(() => subject.complete())
    .catch(e => subject.error(e));

  return subject;
}

loop().subscribe(value => console.log(value));