# Typescript Advanced Types

> Domina el sistema de tipos avanzado de TypeScript: generics, tipos condicionales, mapped types, template literals y utility types para aplicaciones type-safe.

Fuente: https://skillsagentes.com/skills/wshobson/agents/typescript-advanced-types
Markdown: https://skillsagentes.com/skills/wshobson/agents/typescript-advanced-types.md

Repositorio: https://github.com/wshobson/agents
Autor: wshobson
Licencia: MIT
Actualizado: hace 4 meses
Coste de contexto: 76 tok instalada, 2k tok al activarse, 4.3k tok con todos los archivos del bundle
Bundle: 2 archivos, 17 KB
Permisos que pide: ninguno declarado

## Instalación

Un skill son archivos markdown: los mismos archivos valen para cualquier agente y lo único que cambia es el directorio de destino, es decir la bandera `--agent`. Añade `-g` para instalarlo en todos los proyectos de la máquina.

```bash
# Claude Code
npx -y skills add wshobson/agents --skill typescript-advanced-types --agent claude-code
# Cursor
npx -y skills add wshobson/agents --skill typescript-advanced-types --agent cursor
# Codex
npx -y skills add wshobson/agents --skill typescript-advanced-types --agent codex
# Gemini CLI
npx -y skills add wshobson/agents --skill typescript-advanced-types --agent gemini
# Windsurf
npx -y skills add wshobson/agents --skill typescript-advanced-types --agent windsurf
# Cline
npx -y skills add wshobson/agents --skill typescript-advanced-types --agent cline
```

## Qué hace

- Aplica generics, tipos condicionales, mapped types y template literal types en TypeScript
- Construye utilidades de tipos reutilizables y sistemas de inferencia complejos
- Aporta buenas prácticas y errores comunes al diseñar tipos avanzados

## Cuándo usarla

- Construir librerías o frameworks type-safe
- Crear componentes genéricos reutilizables
- Implementar lógica de inferencia de tipos compleja
- Migrar código JavaScript a TypeScript

## Qué la activa

- "Ayúdame a crear un tipo genérico con restricciones en TypeScript"
- "Necesito un mapped type para transformar las propiedades de una interfaz"
- "Cómo hago inferencia de tipos con conditional types en TypeScript"

## Archivos

- SKILL.md — 8 KB
- references/details.md — 9 KB

## SKILL.md

Reproducido tal cual desde wshobson/agents bajo MIT. Esta sección es el documento original y está en inglés.

# TypeScript Advanced Types

Comprehensive guidance for mastering TypeScript's advanced type system including generics, conditional types, mapped types, template literal types, and utility types for building robust, type-safe applications.

## When to Use This Skill

- Building type-safe libraries or frameworks
- Creating reusable generic components
- Implementing complex type inference logic
- Designing type-safe API clients
- Building form validation systems
- Creating strongly-typed configuration objects
- Implementing type-safe state management
- Migrating JavaScript codebases to TypeScript

## Core Concepts

### 1. Generics

**Purpose:** Create reusable, type-flexible components while maintaining type safety.

**Basic Generic Function:**

```typescript
function identity<T>(value: T): T {
  return value;
}

const num = identity<number>(42); // Type: number
const str = identity<string>("hello"); // Type: string
const auto = identity(true); // Type inferred: boolean
```

**Generic Constraints:**

```typescript
interface HasLength {
  length: number;
}

function logLength<T extends HasLength>(item: T): T {
  console.log(item.length);
  return item;
}

logLength("hello"); // OK: string has length
logLength([1, 2, 3]); // OK: array has length
logLength({ length: 10 }); // OK: object has length
// logLength(42);             // Error: number has no length
```

**Multiple Type Parameters:**

```typescript
function merge<T, U>(obj1: T, obj2: U): T & U {
  return { ...obj1, ...obj2 };
}

const merged = merge({ name: "John" }, { age: 30 });
// Type: { name: string } & { age: number }
```

### 2. Conditional Types

**Purpose:** Create types that depend on conditions, enabling sophisticated type logic.

**Basic Conditional Type:**

```typescript
type IsString<T> = T extends string ? true : false;

type A = IsString<string>; // true
type B = IsString<number>; // false
```

**Extracting Return Types:**

```typescript
type ReturnType<T> = T extends (...args: any[]) => infer R ? R : never;

function getUser() {
  return { id: 1, name: "John" };
}

type User = ReturnType<typeof getUser>;
// Type: { id: number; name: string; }
```

**Distributive Conditional Types:**

```typescript
type ToArray<T> = T extends any ? T[] : never;

type StrOrNumArray = ToArray<string | number>;
// Type: string[] | number[]
```

**Nested Conditions:**

```typescript
type TypeName<T> = T extends string
  ? "string"
  : T extends number
    ? "number"
    : T extends boolean
      ? "boolean"
      : T extends undefined
        ? "undefined"
        : T extends Function
          ? "function"
          : "object";

type T1 = TypeName<string>; // "string"
type T2 = TypeName<() => void>; // "function"
```

### 3. Mapped Types

**Purpose:** Transform existing types by iterating over their properties.

**Basic Mapped Type:**

```typescript
type Readonly<T> = {
  readonly [P in keyof T]: T[P];
};

interface User {
  id: number;
  name: string;
}

type ReadonlyUser = Readonly<User>;
// Type: { readonly id: number; readonly name: string; }
```

**Optional Properties:**

```typescript
type Partial<T> = {
  [P in keyof T]?: T[P];
};

type PartialUser = Partial<User>;
// Type: { id?: number; name?: string; }
```

**Key Remapping:**

```typescript
type Getters<T> = {
  [K in keyof T as `get${Capitalize<string & K>}`]: () => T[K];
};

interface Person {
  name: string;
  age: number;
}

type PersonGetters = Getters<Person>;
// Type: { getName: () => string; getAge: () => number; }
```

**Filtering Properties:**

```typescript
type PickByType<T, U> = {
  [K in keyof T as T[K] extends U ? K : never]: T[K];
};

interface Mixed {
  id: number;
  name: string;
  age: number;
  active: boolean;
}

type OnlyNumbers = PickByType<Mixed, number>;
// Type: { id: number; age: number; }
```

### 4. Template Literal Types

**Purpose:** Create string-based types with pattern matching and transformation.

**Basic Template Literal:**

```typescript
type EventName = "click" | "focus" | "blur";
type EventHandler = `on${Capitalize<EventName>}`;
// Type: "onClick" | "onFocus" | "onBlur"
```

**String Manipulation:**

```typescript
type UppercaseGreeting = Uppercase<"hello">; // "HELLO"
type LowercaseGreeting = Lowercase<"HELLO">; // "hello"
type CapitalizedName = Capitalize<"john">; // "John"
type UncapitalizedName = Uncapitalize<"John">; // "john"
```

**Path Building:**

```typescript
type Path<T> = T extends object
  ? {
      [K in keyof T]: K extends string ? `${K}` | `${K}.${Path<T[K]>}` : never;
    }[keyof T]
  : never;

interface Config {
  server: {
    host: string;
    port: number;
  };
  database: {
    url: string;
  };
}

type ConfigPath = Path<Config>;
// Type: "server" | "database" | "server.host" | "server.port" | "database.url"
```

### 5. Utility Types

**Built-in Utility Types:**

```typescript
// Partial<T> - Make all properties optional
type PartialUser = Partial<User>;

// Required<T> - Make all properties required
type RequiredUser = Required<PartialUser>;

// Readonly<T> - Make all properties readonly
type ReadonlyUser = Readonly<User>;

// Pick<T, K> - Select specific properties
type UserName = Pick<User, "name" | "email">;

// Omit<T, K> - Remove specific properties
type UserWithoutPassword = Omit<User, "password">;

// Exclude<T, U> - Exclude types from union
type T1 = Exclude<"a" | "b" | "c", "a">; // "b" | "c"

// Extract<T, U> - Extract types from union
type T2 = Extract<"a" | "b" | "c", "a" | "b">; // "a" | "b"

// NonNullable<T> - Exclude null and undefined
type T3 = NonNullable<string | null | undefined>; // string

// Record<K, T> - Create object type with keys K and values T
type PageInfo = Record<"home" | "about", { title: string }>;
```

## Detailed worked examples and patterns

Detailed sections (starting with `## Advanced Patterns`) live in `references/details.md`. Read that file when the navigation summary above is insufficient.

## Best Practices

1. **Use `unknown` over `any`**: Enforce type checking
2. **Prefer `interface` for object shapes**: Better error messages
3. **Use `type` for unions and complex types**: More flexible
4. **Leverage type inference**: Let TypeScript infer when possible
5. **Create helper types**: Build reusable type utilities
6. **Use const assertions**: Preserve literal types
7. **Avoid type assertions**: Use type guards instead
8. **Document complex types**: Add JSDoc comments
9. **Use strict mode**: Enable all strict compiler options
10. **Test your types**: Use type tests to verify type behavior

## Type Testing

```typescript
// Type assertion tests
type AssertEqual<T, U> = [T] extends [U]
  ? [U] extends [T]
    ? true
    : false
  : false;

type Test1 = AssertEqual<string, string>; // true
type Test2 = AssertEqual<string, number>; // false
type Test3 = AssertEqual<string | number, string>; // false

// Expect error helper
type ExpectError<T extends never> = T;

// Example usage
type ShouldError = ExpectError<AssertEqual<string, number>>;
```

## Common Pitfalls

1. **Over-using `any`**: Defeats the purpose of TypeScript
2. **Ignoring strict null checks**: Can lead to runtime errors
3. **Too complex types**: Can slow down compilation
4. **Not using discriminated unions**: Misses type narrowing opportunities
5. **Forgetting readonly modifiers**: Allows unintended mutations
6. **Circular type references**: Can cause compiler errors
7. **Not handling edge cases**: Like empty arrays or null values

## Performance Considerations

- Avoid deeply nested conditional types
- Use simple types when possible
- Cache complex type computations
- Limit recursion depth in recursive types
- Use build tools to skip type checking in production

## Dónde encaja

- Categoría: [Herramientas para desarrolladores](https://skillsagentes.com/categorias/herramientas-desarrollo.md) — Skills que cambian cómo tu agente escribe, revisa y despliega código.
- Creador: [wshobson](https://skillsagentes.com/creators/wshobson.md) — 183 skills en el directorio
- [Todas las skills](https://skillsagentes.com/skills.md)
- [Ranking de instalaciones](https://skillsagentes.com/ranking.md)

## Otras skills del mismo repositorio

- [Hermes Tweet](https://skillsagentes.com/skills/wshobson/agents/hermes-tweet.md): Instala y opera Hermes Tweet, un plugin de Hermes Agent para investigar X/Twitter, leer timelines, analizar tweets y ejecutar operaciones privadas o de cambio de estado con aprobación previa.
- [Superself](https://skillsagentes.com/skills/wshobson/agents/superself.md): Úsalo cuando un proyecto guarda su estado en Superself: lee `self context` al iniciar sesión, vincula el trabajo a una work unit, reporta con evidencia y registra decisiones confirmadas.
- [Grounded Vault](https://skillsagentes.com/skills/wshobson/agents/grounded-vault.md): Úsalo para mantener un almacén Markdown de conocimiento donde cada afirmación compilada se rastrea hasta una fuente inmutable y el drift se detecta con git diff sin gastar tokens.
- [Postgresql Table Design](https://skillsagentes.com/skills/wshobson/agents/postgresql-table-design.md): Úsalo al diseñar o revisar un esquema específico de PostgreSQL: buenas prácticas, tipos de datos, indexación, restricciones, patrones de rendimiento y funciones avanzadas.
- [Prompt Engineering Patterns](https://skillsagentes.com/skills/wshobson/agents/prompt-engineering-patterns.md): Úsalo cuando pidan optimizar un prompt, mejorar su rendimiento, diseñar una plantilla, aplicar chain-of-thought, few-shot prompting o técnicas avanzadas de prompt engineering para producción.

---

Skills Agentes · [Índice de páginas en markdown](https://skillsagentes.com/sitemap.md) · [Inicio](https://skillsagentes.com/index.md)