There is also a shareReplay operator, which keeps track of the number of observers, and disconnects from the source Observable when that number drops to zero. shareReplay takes three optional parameters and returns an ordinary Observable:

bufferSize

the maximum number of items to buffer and replay to subsequent observers

window

the age, in milliseconds, at which items in this buffer may be discarded without being emitted to subsequent observers

scheduler

the Scheduler on which this operator will operate

Sample Code

var interval = Rx.Observable.interval(1000);

var source = interval
    .take(4)
    .doAction(function (x) {
        console.log('Side effect');
    });

var published = source
    .shareReplay(3);

published.subscribe(createObserver('SourceA'));
published.subscribe(createObserver('SourceB'));

// Creating a third subscription after the previous two subscriptions have
// completed. Notice that no side effects result from this subscription,
// because the notifications are cached and replayed.
Rx.Observable
    .return(true)
    .delay(6000)
    .flatMap(published)
    .subscribe(createObserver('SourceC'));

function createObserver(tag) {
    return Rx.Observer.create(
        function (x) { console.log('Next: ' + tag + x); },
        function (err) { console.log('Error: ' + err); },
        function () { console.log('Completed'); });
}

Side effect
Next: SourceA0
Next: SourceB0
Side effect
Next: SourceA1
Next: SourceB1
Side effect
Next: SourceA2
Next: SourceB2
Side effect
Next: SourceA3
Next: SourceB3
Completed
Completed
Next: SourceC1
Next: SourceC2
Next: SourceC3
Completed

replay and shareReplay are found in the following distributions:

• rx.all.js
• rx.all.compat.js
• rx.binding.js (requires rx.js or rx.compat.js)
• rx.lite.js
• rx.lite.compat.js