Migrating 300k LOC from Flow to TypeScript

After two mostly happy years with Flow, we recently decided to move to TypeScript because of its community support, superior editor experience, and better type coverage. Ultimately we were concerned with the complexity of this approach, that engineers would have to know two different languages to work in the codebase, and that the migration could take a long time and generally add to the complexity of working in the codebase. Fixing Errors
Of course, there were many TypeScript errors in the migrated codebase — over 6,000 in our case — and we decided to ignore the errors with // @ts-ignore comments to get CI green.

Source: medium.com