SEVEN YEARS TO TYPESCRIPT: MIGRATING 11,000 FILES AT PATREON

Summary from the TLDR Dev newsletter

Patreon successfully completed a seven-year migration (2019-2026) of its entire 11,000-file, 1 million-line frontend codebase from JavaScript to TypeScript. The process evolved from an initial grassroots adoption to a dedicated infrastructure development phase, establishing foundational types and CI checks. The final and most accelerated phase, starting in 2025, used AI-powered codemods and advanced workflows to tackle complex legacy code.