Why scheduling matters with RxJS

currentthread.js

Rx.Observable.fromArray([1,2,3], Rx.Scheduler.currentThread)
  .flatMap(function (x) {
    return Rx.Observable.repeat(x, x);
  })
  .subscribe(function (x) {
    console.log('Next: %s', x)
  });

// => Next 1
// => Next 2
// => Next 2
// => Next 3
// => Next 3
// => Next 3

Rx.Observable.fromArray([1,2,3], Rx.Scheduler.immediate)
  .flatMap(function (x) {
    return Rx.Observable.repeat(x, x);
  })
  .subscribe(function (x) {
    console.log('Next: %s', x)
  });
  
// => Next 1
// => Next 2
// => Next 3
// => Next 2
// => Next 3
// => Next 3

Rx.Observable.fromArray([1,2,3], Rx.Scheduler.default)
  .flatMap(function (x) {
    return Rx.Observable.repeat(x, x);
  })
  .subscribe(function (x) {
    console.log('Next: %s', x)
  });

// => Next 1
// => Next 2
// => Next 2
// => Next 3
// => Next 3
// => Next 3