### core-js@2.6.12: core-js@<3.4 is no longer maintained and not recommended for usage due to the
number of issues. Because of the V8 engine whims, feature detection in old core-js versions could cause a slowdown up to 100x even if nothing is polyfilled. Please, upgrade your dependencies to the actual version of core-js.
```shell
core-js 버전 3.3 미만은 유지보수가 안되니 사용하지 말라
# yarn add core-js@^3


# yarn audit  

# yarn add yarn-audit-fix -D
# npx yarn-audit-fix
```