数据结构之 - 字典

let Dictionary = function () {
  let items = {};

  this.has = function (key) {
    return items.hasOwnProperty(key);
  };
  this.set = function (key, value) {
    items[key] = value;
  };
  this.delete = function (key) {
    if (items.has(key)) {
      delete items[key];
      return true;
    }
    return false;
  };

  this.get = function (key) {
    if (items.has(key)) {
      return items[key];
    }
    return undefined;
  };
};