A JavaScript function ("class") that returns an object which can be used to calculate statistics on the the passed numeric Array.

Stats.js

/**
    Returns an object which can be used to calculate statistics on the
    the passed numeric Array.
 */
var Stats = function (arr) {
    arr = arr || [];

    // http://en.wikipedia.org/wiki/Mean#Arithmetic_mean_.28AM.29
    this.arithmeticMean = function () {
        var i, sum = 0;

        for (i = 0; i < arr.length; i += 1) {
            sum += arr[i];
        }

        return sum / arr.length;
    };

    this.mean = this.arithmeticMean;

    // http://en.wikipedia.org/wiki/Mean#Geometric_mean_.28GM.29
    this.geometricMean = function () {
        var i, product = 1;

        for (i = 0; i < arr.length; i += 1) {
            product = product * arr[i];
        }

        return Math.pow(product, (1 / arr.length));
    };

    // http://en.wikipedia.org/wiki/Mean#Harmonic_mean_.28HM.29
    this.harmonicMean = function () {
        var i, sum = 0;

        for (i = 0; i < arr.length; i += 1) {
            sum += (1 / arr[i]);
        }

        return arr.length / sum;
    };

    // http://en.wikipedia.org/wiki/Standard_deviation
    this.stdDev = function () {
        var mean, i, sum = 0;

        mean = this.arithmeticMean();
        for (i = 0; i < arr.length; i += 1) {
            sum += Math.pow(arr[i] - mean, 2);
        }

        return Math.pow(sum / arr.length, 0.5);
    };

    // http://en.wikipedia.org/wiki/Median
    this.median = function () {
        var middleValueId = Math.floor(arr.length / 2);

        return arr.slice().sort(function (a, b) {
            return a - b;
        })[middleValueId];
    };

    return this;
};