RollingAverage.js

function RollingAverage ($config) {
	$config = $config || {};
	this._average = $config.average || 0;
	this._numbers = $config.numbers || 0;
}
RollingAverage.prototype.push = function (number) {
	this._numbers++;
	var weight = 1 / this._numbers;
	this._average += (number - this._average) * weight;
	return this._average;
};