code: function(key) {
      // don't use ES6 "delete" because it will be annoying
      // to use in browsers that are not ES6 friendly;
      var keys = this.keys,
          values = this.values,
          guid = guidFor(key),
          value;
  
      if (values.hasOwnProperty(guid)) {
        keys.remove(key);
        value = values[guid];
        delete values[guid];
        return true;
      } else {
        return false;
      }
    }
docs: Removes a value from the map for an associated key.
  
  @method remove
  @param {anything} key
  @return {Boolean} true if an item was removed, false otherwise