Reactive Programming, medium, sum-example-reactive-working

sum-example-reactive-working.js

const Rx = require('rxjs');

const n$ = new Rx.Observable((observer) => {
  observer.next(2);
  setTimeout(() => {
    observer.next(3);
    observer.complete();
  }, 200);
});

const m$ = Rx.Observable.of(3);

const sum = (acc, x) => acc + x;

const t$ = n$.mergeMap(n => 
  Rx.Observable.of(n)
    .concat(m$)
    .reduce(sum)
);

t$.subscribe(t => {
  console.log(`Result: ${t}`);
});