MIGRATING 3.7 MILLION LINES OF FLOW CODE TO TYPESCRIPT

Summary from the TLDR Web Dev newsletter

Pinterest successfully migrated 3.7 million lines of code from Flow to TypeScript over eight months. The migration used a "big bang" approach using codemods and had three phases: setup, conversion, and integration. Pinterest validated the migration through detailed testing, including daily automated tests, manual testing, and byte-for-byte comparisons of transpiled JavaScript.