MergeSort.js

function MergeSort() { }

MergeSort.prototype.sort = function(values) {
  if (values.length < 2) {
    return values;
  }
    
  var mid = Math.floor(values.length/2);
  var left = this.sort(values.slice(0, mid));
  var right = this.sort(values.slice(mid, values.length));
    
  return this.merge(left, right);
};

MergeSort.prototype.merge = function(left, right) {
  var output = [];
  
  while(left.length > 0 && right.length > 0) {
    if (left[0] > right[0]) {
      output.push(right[0]);
      right.shift();
    } else {
      output.push(left[0]);
      left.shift();
    }
  }
  
  while(left.length > 0) {
    output.push(left[0]);
    left.shift();
  }
  
  while(right.length > 0) {
    output.push(right[0]);
    right.shift();
  }
  
  return output;
};

let sorter = new MergeSort();

console.log(sorter.sort([16,2,30,10,9]));