typescript-engineering

Scan for `any`, non-null assertions (`!`), lying `as` casts including `as unknown as T`, and signatures that hide `undefined` returns. The Skill's anti-pattern catalog assigns each smell a code (T1-T12) with a concrete fix, such as replacing `any` with `unknown` plus a type predicate.

Use `interface` for object contracts meant to be implemented or extended, especially dependency-injection ports. Use `type` for unions, intersections, tuples, mapped or conditional types, and primitive aliases. A discriminated union is always a `type`.

Use a class when you need encapsulated mutable state or an instance satisfying a DI port; otherwise use a plain function. A class with one method and no state is a function in disguise, which the Skill flags as anti-pattern P11.

Yes, the rules scale down. A short script does not need ports, DI, or layered folders, but type honesty, inward-pointing dependencies, and unrepresentable illegal states apply at every size. Rigor is scaled to the code's change pressure.

Floating Promises happen when an async function is called without `await` or explicit handling, silently swallowing rejections. The fix is to await every call, use `Promise.all` for independent operations, and enable ESLint's `no-floating-promises` rule.

Define repository and service interfaces in the domain module that consumes them, then have infrastructure modules implement those ports. Construct concrete implementations only in a single composition root like `main.ts`, keeping the dependency arrow pointing inward.