# Utility Types at a Glance — TypeScript

Source: https://www.geekswithgeeks.com/en/typescript/ts-utility-types

> Built-in helpers that transform an existing type: Partial, Pick, Omit, Record, Readonly.

## Partial & Pick

`Partial<T>` makes every property optional (great for update payloads). `Pick<T, K>` keeps only the listed keys.

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

type UserUpdate = Partial<User>;         // all fields optional
type UserPreview = Pick<User, "id" | "name">; // { id; name }
```

## Omit & Record

`Omit<T, K>` keeps everything except the listed keys. `Record<K, V>` builds an object type mapping every key in `K` to type `V`.

```typescript
type UserNoEmail = Omit<User, "email">;   // { id; name }
type Roles = "admin" | "editor" | "viewer";
type Permissions = Record<Roles, boolean>;
// { admin: boolean; editor: boolean; viewer: boolean }
```

## Readonly<T>

`Readonly<T>` marks every property `readonly`, freezing the type without touching the original.

```typescript
type FrozenUser = Readonly<User>;
const u: FrozenUser = { id: 1, name: "Ada", email: "a@x.com" };
u.name = "Bo";
// Error: Cannot assign to 'name' because it is a read-only property.
```

## Compose them

Utility types nest: `Readonly<Partial<Pick<User, "name" | "email">>>` builds exactly the shape you need without a new interface.