MergeSort implementation in JavaScript

mergesort.js

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);
}