Untitled

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Observable.forkJoin</title>
    <link rel="stylesheet" href="style.css">
    <script src="//unpkg.com/rxjs/bundles/Rx.js"></script>    
</head>
<body>
    <script src="app.js"></script>
</body>
</html>

const {Observable} = Rx
const storiesUrl = 'https://hacker-news.firebaseio.com/v0/topstories.json'
const itemUrl = id => `https://hacker-news.firebaseio.com/v0/item/${id}.json`
const body = document.querySelector('body')


Observable.ajax(storiesUrl).map(e => e.response.slice(0,3))
    .switchMap(ids => Observable.forkJoin(ids.map(id => {
        const url = itemUrl(id)
        return Observable.ajax(url).map(e => e.response)
    })))
    .subscribe(result => result.map(story => {
      body.innerHTML += `<div>${story.title}</div>`
    }))

body{
  font-family: Menlo, monospace;
}