typescriptlisted

# TypeScript Standards Default load: this file only. Pull `refs/tooling.md`, `refs/testing.md`, or `refs/security.md` only when the task explicitly needs that depth. ## Priority: P0 — Type Correctness ### Type Annotations - Explicit params and return types on all public declarations. Infer locals. - Avoid `any`. Prefer `unknown`, generics, or a narrowly-scoped escape hatch with a comment when interop forces it. - Never use the `Function` type. Use a typed signature: `() => void`. ### Interfaces vs Types - `interface` for object shapes that describe APIs — supports declaration merging. - `type` for unions, intersections, mapped types, and conditional types. ### Strict Mode - `strict: true` in tsconfig. On existing repos, migrate incrementally: `strictNullChecks` → `noImplicitAny` → `strictFunctionTypes`. Never flip `strict: true` in one step. - Avoid non-null assertion (`!`). Use narrowing (`typeof`, `instanceof`, if-checks) instead. - `?.` and `??` for null safety — use narrowing, not `!`. ### Enums - Literal unions or `as const` objects. No runtime `enum`. ### Generics - Use generics for reusable, type-safe code. Constrain with `extends` where appropriate. ### Type Guards - Use `typeof`, `instanceof`, and predicate functions (`x is T`) to narrow types. ### Utility Types - Prefer built-ins: `Partial`, `Required`, `Pick`, `Omit`, `Record`, `Readonly`, `NonNullable`. - Prefer `satisfies` for object literals that must conform to a contract without widening the inferred