Rxjsでasync.series相当の処理を行う。

rx-async.js

const Rx = require('rx');


Rx.Observable.prototype.mapParallel = function (fn) {
  return this.concatMap((v) => Rx.Observable.fromNodeCallback(fn)(v));
};

Rx.Observable.prototype.mapSeries = function (fn) {
  return this.concatMap((v) => Rx.Observable.defer(() => Rx.Observable.fromNodeCallback(fn)(v)));
};

Rx.Observable.of(1, 2, 3, 4)
  .mapSeries((v, done) => setTimeout(() => done(null, v), 100))
  .subscribe((v) => console.log(v));