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TS Utility Types

TypeScript provides a set of built-in utility types that help manipulate existing types to create new ones. These types make it easier to work with complex type transformations.

Key Topics

Partial

The Partial utility type makes all properties of a type optional.

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

let partialUser: Partial = { name: "Alice" };
console.log(partialUser); // { name: "Alice" }

Output

{ name: "Alice" }

Explanation: The Partial utility type allows the creation of an object with some properties of the User interface while leaving others undefined.

Readonly

The Readonly utility type makes all properties of a type immutable.

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

const readonlyUser: Readonly = { id: 1, name: "Alice" };
// readonlyUser.id = 2; // Error: Cannot assign to 'id' because it is a read-only property.
console.log(readonlyUser);

Output

{ id: 1, name: "Alice" }

Explanation: The Readonly utility type ensures that the properties of readonlyUser cannot be modified after initialization.

Pick

The Pick utility type allows you to create a new type by selecting specific properties from an existing type.

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

type UserPreview = Pick;

const userPreview: UserPreview = { name: "Alice", email: "alice@example.com" };
console.log(userPreview);

Output

{ name: "Alice", email: "alice@example.com" }

Explanation: The Pick utility type creates a new type UserPreview with only the name and email properties from the User interface.

Omit

The Omit utility type creates a new type by excluding specific properties from an existing type.

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

type UserWithoutEmail = Omit;

const userWithoutEmail: UserWithoutEmail = { id: 1, name: "Alice" };
console.log(userWithoutEmail);

Output

{ id: 1, name: "Alice" }

Explanation: The Omit utility type creates a new type UserWithoutEmail by excluding the email property from the User interface.

Record

The Record utility type constructs a type with a set of keys and values of a specific type.

type Role = "admin" | "user" | "guest";

const roles: Record = {
    admin: "Alice",
    user: "Bob",
    guest: "Charlie",
};
console.log(roles);

Output

{ admin: "Alice", user: "Bob", guest: "Charlie" }

Explanation: The Record utility type creates a type where keys are Role and values are string.

Key Takeaways

  • Partial: Makes all properties optional.
  • Readonly: Prevents modification of properties after initialization.
  • Pick: Creates a type by selecting specific properties.
  • Omit: Creates a type by excluding specific properties.
  • Record: Constructs a type with predefined keys and values.
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