B · ModelingIntermediate30 min read
5. Checkpoint A — Strict types & unions
TypeScript · 44 pages source format
Before generics and utilities, prove strict setup works and you can model real states with unions. Fix gaps before Phase C.
What you'll learn
- Type safety self-check
Pass criteria
- tsconfig strict: true, npm run typecheck script works
- Core utils converted to .ts with typed params and returns
- Domain models (User, Post, etc.) in types/models.ts
- FetchState or Result discriminated union in use
- Zero any (or each any has // ponytail: escape hatch comment)
- Can explain type vs interface in one sentence
Do this now
Audit each criterion. Fix failures before continuing.
Clear?
Error reading drill
Copy 3 compiler errors into notes. Write plain English for each. Fix without Stack Overflow if possible.
Do this now
Intentionally break types. Fix from error messages alone.
Clear?