TypeScript Operational Guide

Enterprise-grade rules for writing resilient, type-safe TypeScript in 2026. Follow these standards when refactoring, writing new code, or configuring projects.

1. Type Safety Mandates

• Never use any: Use unknown for unstructured data and narrow it with strict type guards or typeof/instanceof checks.
• Avoid as assertions: Casting subverts the type system. Use the satisfies operator to validate shape without widening, or use strict type guards to preserve inference.
• Use Unions over Enums: Prefer literal union types (type Status = "active" | "inactive"). Only use const enum when an intentional zero-overhead interop contract is required. Enums create unnecessary runtime footprint and complex mapping issues.
• Boundary Validation: Always use Zod (or equivalent schema validation) to parse unknown data at system boundaries (API payloads, database reads, file I/O). Never blindly cast external payloads.

2. Project Configuration (tsconfig.json)

Unless explicitly directed otherwise by the user or existing ecosystem:

• Module System: Assume an ESM-first setup. Ensure "type": "module" is in package.json.
• Strict Mode: Ensure "strict": true is enabled.
• Module Resolution: Use "moduleResolution": "Bundler" or "Node16" for modern ESM.

3. Generics and Utility Types

• Keep generics constrained (<T extends Record<string, unknown>>) to avoid over-broad type matching.
• Prefer built-in utility types (Record, Partial, Omit, Pick, Awaited) over custom mapped types when possible.
• Use Readonly<T> for props and configurations that shouldn't mutate.

4. Error Handling

• Avoid throwing untyped objects. Throw Error subclasses.
• Use unknown in catch blocks (e.g., catch (error: unknown)) and check error instanceof Error before accessing .message.

5. Security & Linting

• Do not bypass quality checks using @ts-ignore, @ts-expect-error, or @ts-nocheck unless mandated by an unavoidable upstream bug.
• Avoid using eslint-disable to silence legitimate typing complaints.

6. Deep References

For comprehensive tutorials or ecosystem-specific patterns, consult:

• TypeScript Tutorial & Deep Dive