010112 Typescript Rules

TypeScript Rules

Overview

TypeScript 5.7+ language patterns covering strict mode configuration, type safety, advanced typesystem constructs, best practices, Zod validation, and incremental migration from JavaScript.

Quick Reference

Strict Mode

{
  "compilerOptions": {
    "strict": true,
    "noUncheckedIndexedAccess": true,
    "exactOptionalPropertyTypes": true
  }
}

Core Rules

• No any — use unknown, generics, or Record<string, unknown>
• No enum — union literals (type Status = "active" | "inactive") or as const
• No ! non-null assertions — use guards or Result<T, E>
• No @ts-ignore — @ts-expect-error only for intentional error tests
• import type / export type for type-only imports
• Strict equality ===, const by default

Type System

• Discriminated unions for exhaustive checking
• Generics with constraints (<T extends { id: string }>)
• Mapped types (Partial<T>, Immutable<T>, Getters<T>)
• Conditional types (IsString<T>, ArrayElement<T>, Awaited<T>)
• satisfies operator for compile-time validation
• Zod schemas for runtime validation at boundaries

References

• Type Safety — Strict mode, no any, discriminated unions, type guards
• Advanced Types — Generics, mapped types, conditional types, satisfies
• Rules & Anti-Patterns — No enum, import type, Zod, Result pattern, all lint rules (merged)
• Migration Strategy — JS→TS incremental migration, JSDoc, tsconfig
• Code Examples — Repository pattern, DTOs, conditional types, Zod
• Quick Reference — Type system cheat sheet, utility types, keywords