movingAverage.js

function MovingAverage(size) {
	this.buckets = [];
	while (1 + size--) {
		this.buckets.push(0);
	}
	this.i = 0;
	this.average = 0;
}

MovingAverage.prototype.add = function add(n) {
	this.average -= this.buckets[this.i] / this.buckets.length;
	this.buckets[this.i] = n;
	this.average += n / this.buckets.length;
	this.i = this.i === this.buckets.length - 1 ? 0 : this.i + 1;
};

var ma = new MovingAverage(100);

var limit = 1000;
var r = 0;
while (limit--) {
	r = Math.floor(Math.random()*1000) - 500;
	ma.add(r);
	console.log(_Pad(ma.average.toFixed(2), 7), _Pad(r, 7));
}

function _Pad(s, l) {
	return leftPad(s, ' ', l);
}

function leftPad(str, char, len) {
	str = ''+str;
	char = ''+char;
	while (str.length + char.length <= len) {
		str = char + str;
	}
	return str;
}