domains / software-engineering / typescript-advanced-typing / typescript-pro

typescript-pro

Skill card

combined

The three copies overlap on the core task (advanced TypeScript typing, strict configuration, generics/utility types, and build optimization), but each contains material steps or constraints the others lack. Jeffallan/claude-skills adds a concrete 5-step workflow with tsc --noEmit and type-coverage, a reference-loading table, code examples (branded types, discriminated unions, custom utility types), a recommended tsconfig, and explicit MUST/MUST NOT constraints (e.g., no enums, use satisfies, generate declaration files). rmyndharis/antigravity-skills and sickn33/agentic-awesome-skills share a near-identical shorter instruction set (use/do-not-use, 4-step instructions, focus areas, approach, output) and add decorators/metadata, framework integration, TSDoc, and gradual typing, but lack the concrete workflow, examples, and constraints in the Jeffallan copy. Crowning one would hide the alternative approach and the extra constraints/examples, so combine is appropriate.

Repositories

Other copies

Combined skill

---
name: typescript-pro
description: 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.
license: MIT
metadata:
  author: https://github.com/Jeffallan
  company: https://synergetic.solutions
  version: "1.1.0"
  domain: language
  triggers: TypeScript, generics, type safety, conditional types, mapped types, tRPC, tsconfig, type guards, discriminated unions
  role: specialist
  scope: implementation
  output-format: code
  related-skills: fullstack-guardian, api-designer
---

# TypeScript Pro

## Use this skill when

- Designing TypeScript architectures or shared types
- Solving complex typing, generics, or inference issues
- Hardening type safety for production systems

## Do not use this skill when

- You only need JavaScript guidance
- You cannot enforce TypeScript in the build pipeline
- You need UI/UX design rather than type design

## 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:

| Topic | Reference | Load When |
|-------|-----------|-----------|
| Advanced Types | `references/advanced-types.md` | Generics, conditional types, mapped types, template literals |
| Type Guards | `references/type-guards.md` | Type narrowing, discriminated unions, assertion functions |
| Utility Types | `references/utility-types.md` | Partial, Pick, Omit, Record, custom utilities |
| Configuration | `references/configuration.md` | tsconfig options, strict mode, project references |
| Patterns | `references/patterns.md` | Builder pattern, factory pattern, type-safe APIs |

## Code Examples

### Branded Types
```typescript
// 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
```typescript
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
```typescript
// 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
```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
  }
}
```

## Focus Areas
- Advanced type systems (generics, conditional types, mapped types)
- Strict TypeScript configuration and compiler options
- Type inference optimization and utility types
- Decorators and metadata programming
- Module systems and namespace organization
- Integration with modern frameworks (React, Node.js, Express)

## Approach
1. Leverage strict type checking with appropriate compiler flags
2. Use generics and utility types for maximum type safety
3. Prefer type inference over explicit annotations when clear
4. Design robust interfaces and abstract classes
5. Implement proper error boundaries with typed exceptions
6. Optimize build times with incremental compilation

## 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

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

Additionally, ensure output includes:
- Strongly-typed TypeScript with comprehensive interfaces
- Generic functions and classes with proper constraints
- Custom utility types and advanced type manipulations
- Jest/Vitest tests with proper type assertions
- TSConfig optimization for project requirements
- Type declaration files (.d.ts) for external libraries

Support both strict and gradual typing approaches. Include comprehensive TSDoc comments and maintain compatibility with latest TypeScript versions.

## 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

## Limitations
- Use this skill only when the task clearly matches the scope described above.
- Do not treat the output as a substitute for environment-specific validation, testing, or expert review.
- Stop and ask for clarification if required inputs, permissions, safety boundaries, or success criteria are missing.

Maintained by [@jeffallan](https://github.com/jeffallan), Principal Consultant at [Synergetic Solutions](https://synergetic.solutions)

[Documentation](https://jeffallan.github.io/claude-skills/skills/language/typescript-pro/)