1. issue

rn을 실행하기 위해 npm start을 하는 도중 다음 에러가 발생했다.

[Sun Feb 14 2021 13:34:35.430]  ERROR    Invariant Violation: Module AppRegistry is not a registered callable module (calling runApplication)
[Sun Feb 14 2021 13:34:35.440]  ERROR    Invariant Violation: Module AppRegistry is not a registered callable module (calling runApplication)
[Sun Feb 14 2021 13:34:35.450]  ERROR    Invariant Violation: Module AppRegistry is not a registered callable module (calling unmountApplicationComponentAtRootTag)        
[Sun Feb 14 2021 13:34:35.450]  ERROR    Invariant Violation: Module AppRegistry is not a registered callable module (calling runApplication)

2. solution
   module-appregistry-is-not-registered-callable-module-calling-runapplication에 나온대로
   다음 명령어로 문제를 해결했다.

   npm start -- --reset-cache