Airbnb converted many millions of lines gradually using automation and wrote about it: https://medium.com/airbnb-engineering/ts-migrate-a-tool-for-migrating-to

Airbnb converted many millions of lines gradually using automation and wrote about it: https://medium.com/airbnb-engineering/ts-migrate-a-tool-for-migrating-to-typescript-at-scale-cd23bfeb5cc https://medium.com/airbnb-engineering/ts-migrate-a-tool-for-... And also open sourced the tooling: https://github.com/airbnb/ts-migrate https://github.com/airbnb/ts-migrate