https://www.notion.so/juninotion/3-e9f166fff73949d4a1eab40fb04afca5 // Javascript Info_ 'Symbol(심볼형)' 요약 정리
https://www.notion.so/juninotion/4-this-8eaf727d6c674dd3b8602daa4615242b // Javascript Info_ 'Method and 'this'(메서드와 'this')' 요약 정리