merge sort

merge_sort.js

var array = [1, 7, 5, 9, 0, 4, 12, -56, 7, 0, -45, 8, 2, 3, 6, 7, 8, 1, 5, 0,1, 7, 5, 9, 0, 4, 12, -56, 7, 0, -45, 8, 2, 3, 6, 7, 8, 1, 5, 0,1, 7, 5, 9, 0, 4, 12, -56, 7, 0, -45, 8, 2, 3, 6, 7, 8, 1, 5, 0,1, 7, 5, 9, 0, 4, 12, -56, 7, 0, -45, 8, 2, 3, 6, 7, 8, 1, 5, 0,1, 7, 5, 9, 0, 4, 12, -56, 7, 0, -45, 8, 2, 3, 6, 7, 8, 1, 5, 0,1, 7, 5, 9, 0, 4, 12, -56, 7, 0, -45, 8, 2, 3, 6, 7, 8, 1, 5, 0,1, 7, 5, 9, 0, 4, 12, -56, 7, 0, -45, 8, 2, 3, 6, 7, 8, 1, 5, 0];
var merge = function(left, right) {
  var ret = [];
  var length = left.length>right.length? left.length : right.length;
  while(!!left.length || !!right.length) {
    var l = left[0];
    var r = right[0];
    if (l === undefined || l > r) { ret.push(right.shift()); continue;}
    if (r === undefined || r >= l) { ret.push(left.shift()); continue;}
  }
  return ret;
};

var merge_sort = function (unsorted) {
  if (unsorted.length === 1) {
    return unsorted;
  }

  var half = Math.floor(unsorted.length/2);
  var left = unsorted.slice(0, half);
  var right = unsorted.slice(half);
  var sorted_left = merge_sort(left);    
  var sorted_right = merge_sort(right);
  
  return merge(sorted_left, sorted_right);

};

var sorted = merge_sort(array);
console.log(sorted);