javascript merge sort utility

utils.sort.mergesort.js

//Developed by Swapnil Shrikhande
//USAGE
//utils.sort.mergesort([8, 5, 3, 53, 6, 2, 4, 9, 445, 689, 2774, 328, 193, 482],[comparator_function]);

var utils = utils || {};
utils.sort = utils.sort || {};
utils.sort.mergesort = function(list, comparator) {
    if (list.length == 1) {
        return list;
    }
    var leftSorted = utils.sort.mergesort(list.slice(0, list.length / 2), comparator);
    var rightSorted = utils.sort.mergesort(list.slice(list.length / 2, list.length), comparator);
    return utils.sort.merge(leftSorted, rightSorted, comparator);
};
utils.sort.merge = function(left, right, comparator) {
    var sorted = [];
    var totalLength = left.length + right.length;
    var leftIndex = 0;
    var rightIndex = 0;
    for (var index = 0; index < totalLength; index++) {
        if (leftIndex < left.length && rightIndex < right.length) {
            var compareBool = comparator ? comparator(left[leftIndex], right[rightIndex]) 
                                         : left[leftIndex] < right[rightIndex];
            if (compareBool) {
                sorted[index] = left[leftIndex++];
            } else {
                sorted[index] = right[rightIndex++];
            }
        } else if (leftIndex < left.length) {
            sorted[index] = left[leftIndex++];
        } else if (rightIndex < right.length) {
            sorted[index] = right[rightIndex++];
        }
    }
    return sorted;
}