/**
 *  Sort an Array using the Fisher-Yates algorithm.
**/
Array.prototype.shuffle = function() {
  for (var i = this.length - 1; i > 0; i--) {
    var j = Math.floor(Math.random() * i);

    var swap = this[i];
    this[i] = this[j];
    this[j] = swap;
  }

  return this;
}// JavaScript Document