# TypeScript Utility Types

TypeScript provides several global utility types to facilitate common type transformations. These allow you to create new types based on existing ones without rewriting code.

## 1. Partial<Type>

Constructs a type with all properties of `Type` set to **optional**. This is useful when updating objects where you might only change a subset of fields (like a PATCH request).

```typescript
interface User {
  id: number;
  name: string;
  email: string;
}

function updateUser(user: User, fieldsToUpdate: Partial<User>) {
  return { ...user, ...fieldsToUpdate };
}

const user1: User = { id: 1, name: "Alice", email: "alice@example.com" };

// Valid: We only provide 'email', and TypeScript doesn't complain about missing 'id' or 'name'
const user2 = updateUser(user1, { email: "alice@newdomain.com" });
```

## 2. Pick<Type, Keys>

Constructs a type by **picking** a set of properties `Keys` from `Type`. This is useful for creating "preview" objects or DTOs (Data Transfer Objects).

```typescript
interface Todo {
  title: string;
  description: string;
  completed: boolean;
}

type TodoPreview = Pick<Todo, "title" | "completed">;

const todo: TodoPreview = {
  title: "Clean room",
  completed: false,
  // description: "..." // Error: 'description' is not part of TodoPreview
};
```

## 3. Omit<Type, Keys>

The opposite of `Pick`. Constructs a type by picking all properties from `Type` and then **removing** `Keys`.

```typescript
interface Todo {
  title: string;
  description: string;
  completed: boolean;
  createdAt: number;
}

// We want everything EXCEPT 'createdAt'
type TodoInfo = Omit<Todo, "createdAt">;

const todoInfo: TodoInfo = {
  title: "Pick up kids",
  description: "Kindergarten closes at 5pm",
  completed: false
};
```

## 4. Record<Keys, Type>

Constructs an object type whose property keys are `Keys` and whose property values are `Type`. This is cleaner than defining an index signature manually.

```typescript
type CatName = "miffy" | "boris" | "mordred";

const cats: Record<CatName, number> = {
  miffy: 10,
  boris: 5,
  mordred: 16,
};
```

[[programming/javascript/typescript/typescript]]