typescript-expert

Run the included ts_diagnostic.py script from the project root. It checks TypeScript and Node versions, tsconfig strictness flags, detected tooling like ESLint and Vitest, monorepo configuration files, and runs a type check to surface errors.

Use the provided tsconfig-strict.json reference, which enables strict, noUncheckedIndexedAccess, noImplicitOverride, exactOptionalPropertyTypes, and noPropertyAccessFromIndexSignature. It also sets module to ESNext with bundler resolution and skipLibCheck for performance.

The any type disables all type checking and should be avoided, while unknown requires explicit narrowing before use and preserves type safety. The Skill recommends preferring unknown and validating external data at runtime.

No. Types are erased at compile time, so data entering from HTTP requests, queues, environment variables, or external integrations still needs runtime validation with DTOs or schemas aligned to the types.

Use branded types to prevent mixing primitive values like UserId and OrderId that share the same underlying string type. Apply them only when they add real clarity and can be maintained, not as a default pattern.

Double assertions like 'as unknown as' force compilation by bypassing the type checker, hiding real design problems. The Skill treats them as a signal to fix the underlying type or architecture issue instead of masking it.