javascript - How to store accumulated result of a scan with rxjs -

i have 2 merged observables scan after merge. first 1 simple range , other subject. whenever subject emits new value onnext concatenate value in scan , return new array accumulator. if dispose of subscription, , subscribe again replays values range have lost ones subject. in code below want second subscription have final value of [1, 2, 3, 4, 5]

what best way this? right have subject store final value , subscribe that, feels wrong.

here's simple version demonstrates happening:

var rx = require('rx');  var source = rx.observable.range(1, 3);  var adder = new rx.subject();  var merged = source.merge(adder)                     .scan([], function(accum, x) {                         return accum.concat(x);                     });  var subscription1 = merged.subscribe(function(x) {console.log(x)}); adder.onnext(4); adder.onnext(5);  subscription1.dispose();  console.log('after disposal');  var subscription2 = merged.subscribe(function(x) {console.log(x)}); 

this outputs:

[ 1 ] [ 1, 2 ] [ 1, 2, 3 ] [ 1, 2, 3, 4 ] [ 1, 2, 3, 4, 5 ] after disposal [ 1 ] [ 1, 2 ] [ 1, 2, 3 ] 

a subject hot observable, that's why second subscription won't see events coming subject. range observable cold, each "execution instance" entirely owned each subscription. on other hand, subject's "execution instance" singleton , independent, hence second subscription doesn't see events.

there couple of ways of solving this.

1. use replaysubject. have specify buffer size. if don't have limit buffer, using unlimited buffer might cause memory problems.
2. avoid using subject. in other words, avoid using hot observable, replace cold observable, , according problem description gave in beginning, subscriptions wouldn't have problem , see same events. subject can replaced observable, depends on overall architecture. might need rewrite lot. , in worst case, such circular dependency of observables, cannot avoid using subject.
3. rearrange code such subscriptions start before subject starts emitting, subscriptions chance see "live" emissions hot observables.

however, if interpretation of problem correct, need last event emitted merged, use variant of alternative (1) replay last event. matter of adding .sharereplay(1) merged, make hot replayed observable.