define([], function() {

  /** Used for native method references. */
  var objectProto = Object.prototype;

  /** Used to check objects for own properties. */
  var hasOwnProperty = objectProto.hasOwnProperty;

  /**
   * Checks if a cached value for `key` exists.
   *
   * @private
   * @name has
   * @memberOf _.memoize.Cache
   * @param {string} key The key of the entry to check.
   * @returns {boolean} Returns `true` if an entry for `key` exists, else `false`.
   */
  function mapHas(key) {
    return key != '__proto__' && hasOwnProperty.call(this.__data__, key);
  }

  return mapHas;
});