console.clear()

const itemsPerPage = 30

const page = 2

​

​

const source = Rx.Observable

  .ajax('https://hacker-news.firebaseio.com/v0/topstories.json')

  .concatMap(res => Rx.Observable.from(res.response))

  .skip(itemsPerPage * (page - 1))

  .take(itemsPerPage)

  .concatMap(id => Rx.Observable.ajax(`https://hacker-news.firebaseio.com/v0/item/${id}.json`))

  .map(res => res.response)

  .scan((posts, post) => {

    posts.push(post)

    return posts

  }, [])

  .takeLast(1)

​

​

source.subscribe(x => console.log(x))