this is the code to display a bitcoin price every 10 senconds and calculate the average of the last 5 prices retrieved from the HTTP resource.

main-ES2015.js

let BitcoinPrices = [];

$(document).ready(function() {
    let priceIntervalStream = Rx.Observable.interval(1000).flatMap( param => {
         $('#cdDiv').html(param);
        return getPriceStream();
    });
    priceIntervalStream.subscribe( x => {
        $('#lbl-price').html(x.data.total.amount);
        BitcoinPrices.push(x.data.total.amount);

        if(BitcoinPrices.length >= 5){
            displayAvg();
        }
    });
});

function getPriceStream() {
    return $.getJSONAsObservable("/getcurrentprice").select( d => { return d; });
}

function intervalStream() {
    return Rx.Observable.generateWithRelativeTime(
        10,  //initialstate
        x => { return x >= 0; }, //condition
        x => { return x - 1; }, //iterate
        x => { return x; }, //resultSelector
        x => { return 1000; } //timeSelector
        );
}

function displayAvg()
{
    let sum = 0;
    let avg = 0;
    let source = Rx.Observable.fromArray(BitcoinPrices).map((value, index, obs) =>
    {
        //return only the latest 5 array values.
        if( index > Math.abs(BitcoinPrices.length - 5) ){
            return value;
        }else{
          return 0;
        }
    });

    let subscription = source.subscribe( x => sum += parseFloat(x) );
    avg =  sum / 5;
    $('#avgValue').html(avg.toFixed(2));
}