Javascript에서의 클로저를 이용해서 완벽한 싱글톤만들기

Reference Link:

https://ideveloper2.tistory.com/160 https://www.zerocho.com/category/JavaScript/post/57541bef7dfff917002c4e86 http://steadypost.net/post/lecture/id/13/ http://projectl33t.xyz/archives/50763