irokhes

clock = sinon.useFakeTimers(new Date(2016,11,1).getTime());
new Date(); //=> return the fake Date 'Sat Nov 01 2016 00:00:00'

clock.restore();
new Date(); //=> will return the real time again (now)

stekhn

function weightedMean(arrValues, arrWeights) {

  var result = arrValues.map(function (value, i) {

    var weight = arrWeights[i];
    var sum = value * weight;

    return [sum, weight];
  }).reduce(function (p, c) {