typescript-ultimate

name	typescript-ultimate
description	End-to-end TypeScript engineering skill for designing, implementing, reviewing, and refactoring production-grade TS codebases. Use when tasks involve TypeScript architecture, advanced typing, strict safety, API/schema typing, React/Node/Nest/Express/Fastify patterns, testing, linting, migration, or code review in .ts/.tsx projects.

TypeScript Ultimate

Execute TypeScript work with maximum safety, clarity, and maintainability.

Workflow

1. Identify context first

   • Determine runtime: Node / Browser / React / Next / Nest / Express / Fastify / Deno / RN.
   • Determine strictness target: incremental vs strict-by-default.
   • Determine risk class: API contract, persistence, auth, payments, migrations are high-risk.

2. Lock quality baseline before coding

   • Apply strict compiler profile from references/01-compiler-and-quality-baseline.md.
   • Apply lint and ordering rules from references/07-code-review-and-standards.md.
   • Define typed boundaries for IO and external systems.

3. Model domain types first

   • Design discriminated unions for state and protocol variants.
   • Use utility/mapped/conditional/template-literal types where they reduce duplication.
   • Keep types readable; split deeply complex helpers into named aliases.

4. Implement with type-safe boundaries

   • Parse unknown inputs to validated domain types.
   • Keep any out of core paths.
   • Encode API request/response contracts in types.

5. Verify behavior + type contracts

   • Add runtime tests + type tests (tsc --noEmit, or expect-type style checks).
   • Add edge-case checks for nullability, narrowing, and exhaustive handling.

6. Review against production checklist

   • Use references/07-code-review-and-standards.md review rubric.
   • Prefer smallest safe change that improves type confidence.

Mandatory Rules

• Prefer unknown over any.
• Prefer narrowing/type guards over assertions (as).
• Use discriminated unions for state machines and branching models.
• Keep imports organized and type-only imports explicit (import type).
• Use const by default; avoid mutation when practical.
• Use exhaustive checks (never) for union switches.
• Keep compiler+lint green before completion.

Reference Map

• Compiler/strict baseline: references/01-compiler-and-quality-baseline.md
• Type system patterns: references/02-advanced-type-system.md
• API/schema/contracts: references/03-api-and-schema-typing.md
• Framework-specific patterns: references/04-framework-playbooks.md
• Data/persistence/runtime boundaries: references/05-data-and-runtime-boundaries.md
• Testing strategy: references/06-testing-types-and-behavior.md
• Code review standards: references/07-code-review-and-standards.md
• Source corpus index (downloaded posts): references/source-corpus-index.md

Execution Guidance

• For small fixes: apply minimal patch + enforce local invariants.
• For medium changes: establish/repair types first, then implementation.
• For large migrations: convert module-by-module, maintain compatibility adapters, and increase strictness in stages.
• If runtime/library constraints conflict with strict typing, document trade-offs and isolate unsafe edges.