Reference Link:
https://www.zerocho.com/category/Javascript/post/5740531574288ebc5f2ba97e
https://medium.com/@khwsc1/%EB%B2%88%EC%97%AD-%EC%9E%90%EB%B0%94%EC%8A%A4%ED%81%AC%EB%A6%BD%ED%8A%B8-%EC%8A%A4%EC%BD%94%ED%94%84%EC%99%80-%ED%81%B4%EB%A1%9C%EC%A0%80-javascript-scope-and-closures-8d402c976d19