code: private function parseObject($isConst)
      {
          $start = $this->lexer->token;
          $this->expect(Token::BRACE_L);
          $fields = [];
          while (! $this->skip(Token::BRACE_R)) {
              $fields[] = $this->parseObjectField($isConst);
          }
  
          return new ObjectValueNode([
              'fields' => new NodeList($fields),
              'loc'    => $this->loc($start),
          ]);
      }
docs: @param bool $isConst
  
  @return ObjectValueNode