Lessons Learned Converting Snyk Codebase to TypeScript
summary
Snyk spends 18 months migrating a 300‑repo codebase to TypeScript and reports concrete wins and costs: a one‑day prototype, 300 repos tracked by a script, a necessary forked tap to run tests with ts‑node, 10–14s incremental compile slowdowns until removed allowJs, and a switch from tap to jest. The migration yields immediate bug finds (unused params, wrong shapes), easier refactors via shared types, and a gradual convert‑as‑you‑touch strategy with measurable progress.
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chapters (17)
- 0:00Start
- 3:09Union Type
- 4:38Intersection Type
- 5:20Interface inside an interface
- 6:04Enums
- 6:59Type checking
- 7:28Unused code
- 7:39Type inference
- 8:10Signature hints
- 9:12tsconfig.json
- 10:26Custom Tap script
- 15:32Example conversion js = ts
- 20:39Random extra parameters
- 22:30Cat type
- 22:49Animal type
- 23:00Cat API body type
- 24:01Cat Service
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