<script src="https://cdnjs.cloudflare.com/ajax/libs/rxjs/5.5.2/Rx.min.js"></script>

<button id="foo">Foo</button>
<button id="bar">Bar</button>

<script>
  let {Observable: O} = Rx

  let fooNode = document.querySelector("#foo")
  let barNode = document.querySelector("#bar")

  let fooClick$ = O.fromEvent(fooNode, "click")
    .do(() => { console.log("foo clicked!") })

  let barClick$ = O.fromEvent(barNode, "click")
    .do(() => { console.log("bar clicked!") }).shareReplay(1) // !!! 

  let fooSb = fooClick$.subscribe()
  let barSb = barClick$.subscribe() // !!!

  setTimeout(() => {
    fooSb.unsubscribe()
  }, 2000)

  setTimeout(() => {
    barSb.unsubscribe() // !!!
  }, 2000)
</script>