function mergeSort (arr) {
    if (arr.length < 2) {
      return arr;
    }

    var mid = Math.floor(arr.length / 2);
    var subLeft = mergeSort(arr.slice(0, mid));
    var subRight = mergeSort(arr.slice(mid));

    return merge(subLeft, subRight);
}

function merge (node1, node2) {
    var result = [];
    while (node1.length > 0 && node2.length > 0)
        result.push(node1[0] < node2[0]? node1.shift() : node2.shift());
    return result.concat(node1.length? node1 : node2);
}