https://ponyfoo.com/articles/null-propagation-operator
origin - http://www.pipiscrew.com/2017/08/null-propagation-operator-in-javascript/ null-propagation-operator-in-javascript
https://ponyfoo.com/articles/null-propagation-operator
origin - http://www.pipiscrew.com/2017/08/null-propagation-operator-in-javascript/ null-propagation-operator-in-javascript