Randomly pick an array element with weighted chances

pick-weighted.js

function pickWeighted(array) {
    var n = Math.random(),
        totalChances = 0,
        total = 0,
        result;
    array = array.map(function(row) {
        var min, max;
        var chance = typeof row == 'object' || typeof row == 'function' ? row.chance : 1;
        if (chance) {
            min = totalChances;
            max = totalChances + chance;
            totalChances += chance;
        } else {
            min = max = -1;
        }
        return {
            min: min,
            max: max,
            value: typeof row == 'object' || typeof row == 'function' ? row.value : row
        };
    });
    for(var c in array) {
        var row = array[c];
        if ((row.min / totalChances) <= n && (row.max / totalChances) > n) {
            return row.value;
            break;
        }
    }
}

usage.js

/* Basic Usage: */
pickWeighted([1,2,3])
// => 2

pickWeighted([1,2,3])
// => 3

pickWeighted([1,2,3])
// => 2

pickWeighted([1,2,3])
// => 1

/* Weighted Usage: */
pickWeighted([
   {chance: 0.1, value: 1},
   {chance: 0.5, value: 2},
   {chance: 0.4, value: 3},
]);
// => 2

pickWeighted([
   {chance: 0.1, value: 1},
   {chance: 0.5, value: 2},
   {chance: 0.4, value: 3},
]);
// => 3

pickWeighted([
   {chance: 0.1, value: 1},
   {chance: 0.5, value: 2},
   {chance: 0.4, value: 3},
]);
// => 2