var subject = new Rx.AsyncSubject();

// Subject

// ReplaySubject: replays many, before or after completion

// BehaviorSubject: replays one, only before completion

// AsyncSubject: replays one, only if completed

var observerA = {

  next: function (x) { console.log('A next ' + x); },

  error: function (err) { console.log('A error ' + err); },

  complete: function () { console.log('A done'); },

};

subject.subscribe(observerA);

console.log('observerA subscribed');

var observerB = {

  next: function (x) { console.log('B next ' + x); },

  error: function (err) { console.log('B error ' + err); },

  complete: function () { console.log('B done'); },

};

setTimeout(() => subject.next(), );

setTimeout(() => subject.next(), );

setTimeout(() => subject.next(), );

setTimeout(() => subject.complete(), );

/*

----1---2---3--|

  .............3|

                   3|

*/

setTimeout(function () {

  subject.subscribe(observerB);

  console.log('observerB subscribed');

}, );

/*

"observerA subscribed"

"A next 3"

"A done"

"B next 3"

"B done"

"observerB subscribed"

*/