hoverFetch.js

const fetchContent = (url) =>
    rx.Observable.create(observer => 
      fetch(url)
        .then(res => res.json())
        .then(json => {
          observer.onNext(json)
          observer.onCompleted()
        )
        .catch(e => observer.onError())
    )
    
const hover$ = rx.Observable.fromEvent(myButton, 'mouseover');
const leave$ = rx.Observable.fromEvent(myButton, 'mouseout');
const click$ = rx.Observable.fromEvent(myButton, 'click');

const hoverRequest$ = hover$
  .flatMap(e => 
    fetchContent(e.target.href).takeUntil(leave$)
  )
  
const displayData$ = click$
  .withLatestFrom(hoverRequest$)
  .filter(([click, json]) => !!json)
  .map(([click, json]) => json)
  
displayData$.subscribe(json => console.log(json))