RxJs bitcoin stock ticker example

rx-bitcoin-price-ticker.js

Rx.Observable.timer(0, 10 * 1000)
  .switchMap(_ => fetch('https://blockchain.info/ticker?cors=true')
                    .then(res => res.json())
                    .then(parsed => parsed.EUR.buy)
  )
  .distinctUntilChanged()
  .scan((acc, curr) => ({
      delta: Math.round((acc.value - curr || 0) * 100) / 100,
      value: curr
    }), {})
  .subscribe(tick => console.log(`1 BTC = ${tick.value} EUR (Δ ${tick.delta > 0 ? '+' : ''}${tick.delta})`));