text: function ItemList() {
    this._items = [];
  }
  
  ItemList.prototype.getItems = function(){
    return this._items;
  };
  
  ItemList.prototype.addItem = function(item) {
    this._items.push(item);
  }
  
  ItemList.prototype.deleteItem = function(number){
    this._items.splice(number - 1, 1);
  }
  
  ItemList.prototype.updateItem = function(number, text) {
    var item = this._items[number - 1];
    return item.setText(text);
  }
  