Standard deviation(STDEV) with JavaScript

stdev.js

var stdev = function(arr) {
    var n = arr.length;
    var sum = 0;

    arr.map(function(data) {
        sum+=data;
    });

    var mean = sum / n;

    var variance = 0.0;
    var v1 = 0.0;
    var v2 = 0.0;

    if (n != 1) {
        for (var i = 0; i<n; i++) {
            v1 = v1 + (arr[i] - mean) * (arr[i] - mean);
            v2 = v2 + (arr[i] - mean);
        }

        v2 = v2 * v2 / n;
        variance = (v1 - v2) / (n-1);
        if (variance < 0) { variance = 0; }
        stddev = Math.sqrt(variance);
    }

    return {
        mean: Math.round(mean*100)/100,
        variance: variance,
        deviation: Math.round(stddev*100)/100
    };
};