code: function(attrs, first) {
        if (!attrs || !Object.keys(attrs).length) return first ? void 0 : [];
        return this[first ? 'find' : 'filter'](function(model) {
          for (var key in attrs) {
            if (attrs[key] !== model.get(key)) return false;
          }
          return true;
        });
      }
docs: Return models with matching attributes. Useful for simple cases of `filter`.