code: function(key) {
          if (this.size === 0) { return false; }
          // don't use ES6 "delete" because it will be annoying
          // to use in browsers that are not ES6 friendly;
          var keys = this.keys;
          var values = this.values;
          var guid = guidFor(key);
  
          if (keys["delete"](key, guid)) {
            delete values[guid];
            this.size = keys.size;
            return true;
          } else {
            return false;
          }
        }
docs: Removes a value from the map for an associated key.
  
  @method delete
  @param {*} key
  @return {Boolean} true if an item was removed, false otherwise