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function Queue() {
  this._oldestIndex = 1;
  this._newestIndex = 1;
  this._storage = {};
}

Queue.prototype.size = function () {
  return this._newestIndex - this._oldestIndex;
}

Queue.prototype.enqueue = function(data) {
  this._storage[this._newestIndex] = data;
  this._newestIndex++;
};

Queue.prototype.dequeue = function() {
  var oldestIndex = this._oldestIndex,
      newestIndex = this._newestIndex,
      deletedData;

  if (oldestIndex !== newestIndex) {
    deletedData = this._storage[oldestIndex];
    delete this._storage[oldestIndex];
    this._oldestIndex++;

    return deletedData;
  }
};