TS Type Guard



[TS Custom Type Guard](https://texonom.com/ts-custom-type-guard-1925145a126d40479335092d5ffb23b2)


[Type Proposition Type](https://texonom.com/type-proposition-type-7f2c84bc90ea4268b867f5d0c6c7c041)

- if
> - typeof
> - instanceof
> - ===
> - in
>> ```typeinterface A { x: number }interface B { y: string }function doStuff(q: A | B) {  if ('x' in q)  else }```
> 



> [타입 가드](https://radlohead.gitbook.io/typescript-deep-dive/type-system/typeguard)





