TypeScript — Type Safety Practice

• · TS1 — strict: true in tsconfig from project start; retrofitted incrementally if inherited loose.
• · TS2 — any is never used without an explicit, reviewed justification comment; prefer unknown + narrowing.
• · TS3 — State with mutually exclusive variants is modeled as a discriminated union, not multiple optional fields.
• · TS4 — External data (API responses, form input, env vars) is validated against a schema at the boundary (Zod/io-ts/similar), not cast.
• · TS5 — Function signatures express real constraints (non-empty arrays, branded IDs) rather than the loosest type that compiles.

• · Grep for any and as — each is a candidate for narrowing to a real type.
• · Multiple optional booleans on one type (isLoading?, isError?, data?) → likely should be a discriminated union ({status:'loading'} | {status:'error',error} | {status:'success',data}).
• · Data crossing a network/file/env boundary without a schema validator → add one; don't trust JSON.parse(...) as MyType.
• · A function accepting string when it really means "a UUID" or "an email" → consider a branded type if misuse is a real risk.

• · as MyType casting API responses — no runtime validation, type is a lie at the boundary.
• · any escape hatches accumulating — each one disables checking for everything downstream.
• · Boolean flag soup for state — {isLoading, isError, hasData} allowing impossible combinations (isLoading && isError).
• · // @ts-ignore instead of fixing the type — silences the error without addressing the underlying issue.
• · Non-null assertion (!) as a habit — bypassing null checks the type system correctly flagged.

• [ ] strict mode enabled. (TE1)
• [ ] No unjustified any. (TE2)
• [ ] External data schema-validated at the boundary. (TE3)
• [ ] Mutually exclusive state modeled as discriminated unions. (TE4)
• [ ] Type assertions rare and justified. (TE5)
• [ ] No any/unknown leaking into public API surfaces. (TE6)

• TypeScript Handbook

Este pack cita las siguientes fuentes registradas en el índice bibliográfico:

• webTypeScript HandbookMicrosoft
• webZod documentation