Convert a JS Project to TypeScript (Project-Based Learning) vs TypeScript Official Handbook (typescriptlang.org)

The Handbook walks you through TypeScript's type system in a deliberate sequence — primitives, interfaces, generics, utility types — so each concept builds on the last. The project conversion method drops you into a codebase full of red errors with no map. That's exhilarating if you have context, genuinely demoralizing if you don't. The method builds faster intuition, but only after the Handbook gives you enough vocabulary to understand what the compiler is actually complaining about.

Microsoft maintains the Handbook in lockstep with TypeScript releases, so when TypeScript 5.x ships new features, the docs reflect them. When you convert an old JavaScript project, you're learning TypeScript through the lens of whatever patterns that codebase used — which may be outdated, poorly structured, or actively fighting the type system. You can accidentally learn to work around TypeScript rather than with it.

The r/typescript community specifically recommends enabling strict mode when converting a project, and they're right — it forces you to actually understand the type system instead of papering over it with 'any'. But strict mode on a real codebase can generate hundreds of errors simultaneously, and without foundational knowledge, you'll fix them mechanically without understanding why. The Handbook teaches you what strict mode is enforcing before you have to fight it.

After you've learned TypeScript, the Handbook remains useful forever as a reference you return to when you forget how conditional types work or need to look up a utility type. The project conversion method is a one-time learning experience — once your project is converted, the method is done. The Handbook has compounding value; the project method has a higher learning spike but a shorter shelf life as a resource.