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typescript-pro

Implements advanced TypeScript type systems, creates custom type guards, utility types, and branded types, and configures tRPC for end-to-end type safety. Use when building TypeScript applications requiring advanced generics, conditional or mapped types, discriminated unions, monorepo setup, or full-stack type safety with tRPC.

92

1.07x
Quality

100%

Does it follow best practices?

Impact

85%

1.07x

Average score across 6 eval scenarios

SecuritybySnyk

Passed

No known issues

SKILL.md
Quality
Evals
Security

TypeScript Pro

Core Workflow

  1. Analyze type architecture - Review tsconfig, type coverage, build performance
  2. Design type-first APIs - Create branded types, generics, utility types
  3. Implement with type safety - Write type guards, discriminated unions, conditional types; run tsc --noEmit to catch type errors before proceeding
  4. Optimize build - Configure project references, incremental compilation, tree shaking; re-run tsc --noEmit to confirm zero errors after changes
  5. Test types - Confirm type coverage with a tool like type-coverage; validate that all public APIs have explicit return types; iterate on steps 3–4 until all checks pass

Reference Guide

Load detailed guidance based on context:

TopicReferenceLoad When
Advanced Typesreferences/advanced-types.mdGenerics, conditional types, mapped types, template literals
Type Guardsreferences/type-guards.mdType narrowing, discriminated unions, assertion functions
Utility Typesreferences/utility-types.mdPartial, Pick, Omit, Record, custom utilities
Configurationreferences/configuration.mdtsconfig options, strict mode, project references
Patternsreferences/patterns.mdBuilder pattern, factory pattern, type-safe APIs

Code Examples

Branded Types

// Branded type for domain modeling
type Brand<T, B extends string> = T & { readonly __brand: B };
type UserId  = Brand<string, "UserId">;
type OrderId = Brand<number, "OrderId">;

const toUserId  = (id: string): UserId  => id as UserId;
const toOrderId = (id: number): OrderId => id as OrderId;

// Usage — prevents accidental id mix-ups at compile time
function getOrder(userId: UserId, orderId: OrderId) { /* ... */ }

Discriminated Unions & Type Guards

type LoadingState = { status: "loading" };
type SuccessState = { status: "success"; data: string[] };
type ErrorState   = { status: "error";   error: Error };
type RequestState = LoadingState | SuccessState | ErrorState;

// Type predicate guard
function isSuccess(state: RequestState): state is SuccessState {
  return state.status === "success";
}

// Exhaustive switch with discriminated union
function renderState(state: RequestState): string {
  switch (state.status) {
    case "loading": return "Loading…";
    case "success": return state.data.join(", ");
    case "error":   return state.error.message;
    default: {
      const _exhaustive: never = state;
      throw new Error(`Unhandled state: ${_exhaustive}`);
    }
  }
}

Custom Utility Types

// Deep readonly — immutable nested objects
type DeepReadonly<T> = {
  readonly [K in keyof T]: T[K] extends object ? DeepReadonly<T[K]> : T[K];
};

// Require exactly one of a set of keys
type RequireExactlyOne<T, Keys extends keyof T = keyof T> =
  Pick<T, Exclude<keyof T, Keys>> &
  { [K in Keys]-?: Required<Pick<T, K>> & Partial<Record<Exclude<Keys, K>, never>> }[Keys];

Recommended tsconfig.json

{
  "compilerOptions": {
    "target": "ES2022",
    "module": "NodeNext",
    "moduleResolution": "NodeNext",
    "strict": true,
    "noUncheckedIndexedAccess": true,
    "noImplicitOverride": true,
    "exactOptionalPropertyTypes": true,
    "isolatedModules": true,
    "declaration": true,
    "declarationMap": true,
    "incremental": true,
    "skipLibCheck": false
  }
}

Constraints

MUST DO

  • Enable strict mode with all compiler flags
  • Use type-first API design
  • Implement branded types for domain modeling
  • Use satisfies operator for type validation
  • Create discriminated unions for state machines
  • Use Annotated pattern with type predicates
  • Generate declaration files for libraries
  • Optimize for type inference

MUST NOT DO

  • Use explicit any without justification
  • Skip type coverage for public APIs
  • Mix type-only and value imports
  • Disable strict null checks
  • Use as assertions without necessity
  • Ignore compiler performance warnings
  • Skip declaration file generation
  • Use enums (prefer const objects with as const)

Output Templates

When implementing TypeScript features, provide:

  1. Type definitions (interfaces, types, generics)
  2. Implementation with type guards
  3. tsconfig configuration if needed
  4. Brief explanation of type design decisions

Knowledge Reference

TypeScript 5.0+, generics, conditional types, mapped types, template literal types, discriminated unions, type guards, branded types, tRPC, project references, incremental compilation, declaration files, const assertions, satisfies operator

Repository
jeffallan/claude-skills
Commit

5b76101

Last updated
Created

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