Effective JavaScript 項目45

45.js

function Dict(elements) {
  this.elements = elements || {};
  this.hasSpecialProto = false;
  this.specialProto = undefined;
}

Dict.prototype.has = function (key) {
  if (key === "__proto__") {
    return this.hasSpecialProto;
  }
  return {}.hasOwnProperty.call(this.elements, key);
};

Dict.prototype.get = function (key) {
  if (key === "__proto__") {
    return this.specialProto;
  }
  return this.has(key) ? this.elements[key] : undefined;
};

Dict.prototype.set = function (key) {
  if (key === "__proto__") {
    this.hasSpecialProto = true;
    this.specialProto = val;
  } else {
    this.elements[key] = val;
  }
};

Dict.prototype.remove = function (key) {
  if (key === "__proto__") {
    this.hasSpecialProto = false;
    this.specialProto = undefined;
  } else {
    delete this.elements[key];
  }
};