---
name: typescript-magician-5ae7057a8f87
description: Designs complex generic types, refactors `any` types to strict alternatives, creates type guards and utility types, and resolves TypeScript compiler errors. Use when the user asks about TypeScript (TS) types, generics, type inference, type guards, removing `any` types, strict typing, type errors, `infer`, `extends`, conditional types, mapped types, template literal types, branded/opaque types, or utility types like `Partial`, `Record`, `ReturnType`, and `Awaited`.
metadata:
  tags: typescript, types, generics, type-safety, advanced-typescript
---

## When to use

Use this skill for:
- TypeScript errors and type challenges
- Eliminating `any` types from codebases
- Complex generics and type inference issues
- When strict typing is needed

## Instructions

When invoked:
1. Run `tsc --noEmit` to capture the full error output before making changes
2. Identify the root cause of type issues (unsound inference, missing constraints, implicit `any`, etc.)
3. Craft precise, type-safe solutions using advanced TypeScript features
4. Eliminate all `any` types with proper typing — validate each replacement still satisfies call sites
5. Confirm the fix compiles cleanly with a second `tsc --noEmit` pass

Capabilities include:
- Advanced generics and conditional types
- Template literal types and mapped types
- Utility types and type manipulation
- Brand types and nominal typing
- Complex inference patterns
- Variance and distribution rules
- Module augmentation and declaration merging

For every TypeScript challenge:
- Explain the type theory behind the problem
- Provide multiple solution approaches when applicable
- Show before/after type representations
- Include comprehensive type tests
- Ensure full IntelliSense support

## Quick Examples

### Eliminating `any` with generics

**Before**
```ts
function getProperty(obj: any, key: string): any {
  return obj[key];
}
```

**After**
```ts
function getProperty<T, K extends keyof T>(obj: T, key: K): T[K] {
  return obj[key];
}
// getProperty({ name: "Alice" }, "name") → inferred as string ✓
```

### Narrowing an unknown API response

**Before**
```ts
async function fetchUser(): Promise<any> {
  const res = await fetch("/api/user");
  return res.json();
}
```

**After**
```ts
interface User { id: number; name: string }

function isUser(value: unknown): value is User {
  return (
    typeof value === "object" &&
    value !== null &&
    "id" in value &&
    "name" in value
  );
}

async function fetchUser(): Promise<User> {
  const res = await fetch("/api/user");
  const data: unknown = await res.json();
  if (!isUser(data)) throw new Error("Invalid user shape");
  return data;
}
```

## Reference

Read individual rule files for detailed explanations and code examples:

### Core Patterns
- [rules/as-const-typeof.md](rules/as-const-typeof.md) - Deriving types from runtime values using `as const` and `typeof`
- [rules/array-index-access.md](rules/array-index-access.md) - Accessing array element types using `[number]` indexing
- [rules/utility-types.md](rules/utility-types.md) - Built-in utility types: Parameters, ReturnType, Awaited, Omit, Partial, Record

### Advanced Generics
- [rules/generics-basics.md](rules/generics-basics.md) - Fundamentals of generic types, constraints, and inference
- [rules/builder-pattern.md](rules/builder-pattern.md) - Type-safe builder pattern with chainable methods
- [rules/deep-inference.md](rules/deep-inference.md) - Achieving deep type inference with F.Narrow and const type parameters

### Type-Level Programming
- [rules/conditional-types.md](rules/conditional-types.md) - Conditional types for type-level if/else logic
- [rules/infer-keyword.md](rules/infer-keyword.md) - Using `infer` to extract types within conditional types
- [rules/template-literal-types.md](rules/template-literal-types.md) - String manipulation at the type level
- [rules/mapped-types.md](rules/mapped-types.md) - Creating new types by transforming existing type properties

### Type Safety Patterns
- [rules/opaque-types.md](rules/opaque-types.md) - Brand types and opaque types for type-safe identifiers
- [rules/type-narrowing.md](rules/type-narrowing.md) - Narrowing types through control flow analysis
- [rules/function-overloads.md](rules/function-overloads.md) - Using function overloads for complex function signatures

### Debugging
- [rules/error-diagnosis.md](rules/error-diagnosis.md) - Strategies for diagnosing and understanding TypeScript type errors


---
Source attribution: mcollina
Original project: https://github.com/mcollina/skills/blob/c75d70dbfbe991d8cec42aeda0b64ff14fbb9ac7/skills/typescript-magician/SKILL.md
License: MIT
License information: https://opensource.org/license/mit
Original upstream instructions; downloaded from Mega AI Hub.

## Upstream license notice

MIT License

Copyright (c) 2026 Matteo Collina

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.



# Mega AI Hub resource metadata

Creator / publisher: mcollina
Original project: https://github.com/mcollina/skills/blob/c75d70dbfbe991d8cec42aeda0b64ff14fbb9ac7/skills/typescript-magician/SKILL.md
Attribution basis: Source repository record

Fields of work: Development & Engineering
Roles: Backend Developer, Data Engineer, Frontend Developer, Full-Stack Developer, ML / AI Engineer
Specialties: API, Backend, Cross Platform
Tools: Tool not specified
Country applicability: Country not specified
Classification basis: Source catalog labels
Instruction SHA-256: c0480f756dd5d1e4c7cc2071074a01db63065e9a28f724eb74eb7fafc7b440c4