JS Ergonomic brand check
[JS in Operator](https://texonom.com/js-in-operator-267c1f0930db4962ac8d87af6794b561) [JS Private Variable](https://texonom.com/js-private-variable-35aa9a8cdabd446ca2551cd47fb2cb7f) 


private variable 도 가능
```type'adsf' in  instance```











