TypeScript Utility Types

TypeScript consists of several predefined generic types known as Utility Types. These utility types are useful for manipulating or creating new types more efficiently.

Partial

Partial is a utility type that is used to create a type where all properties are marked as optional.

Syntax

A partial is written as:

Partial<T>;

Where T is the typo you want to make all the properties optional.

Partial Example

In this example, all the properties of the User interface are optional:

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

const partialUser: Partial<User> = {
  name: 'John',
};

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Required

Required is a utility type that is used to create a type with all properties of T marked as Required. It is the opposite of Partial.

Syntax

Required in Typescript is written as:

Required<T>;

Where T is the typo you want to make all the properties mandatory.

Required Example

In this example, all the properties of the User interface (including the optional properties) are made mandatory:

interface User {
  name: string;
  age?: number;
}

const requiredUser: Required<{ name: string; age: number }> = {
  name: 'John',
  age: 25,
};

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Readonly

Readonly is a utility type that marks all the properties in T as readonly, preventing any reassignment.

Syntax

Readonly is written as:

Readonly<T>;

Where properties of T is marked as Readonly.

Readonly Example

In this example, attempting to reassign the value of readonlyUser.age generates an error:

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

const readonlyUser: Readonly<User> = {
  name: 'John',
  age: 30,
};

readonlyUser.age = 31; // Error: Cannot assign to 'age' because it is a read-only property.

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Pick

Pick allows you to create a new type by selecting a set of properties K from an existing type T.

Syntax

Pick is written as:

Pick<T, K>;

where K are the properties you want to include from T.

Pick Example

In this example, Pick is used to create a type from User that includes only the name and email fields, omitting age, without needing to declare a new interface:

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

const pickedUser: Pick<User, 'name' | 'email'> = {
  name: 'John',
  email: '[email protected]',
};

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Omit

Omit allows you to create a new type by excluding a set of properties K from an existing type T.

Syntax

Omit is written as:

Omit<T, K>;

where K properties are omitted from T.

Omit Example

In this example, we removed the age property from the User interface:

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

const omittedUser: Omit<User, 'age'> = {
  name: 'John',
  email: '[email protected]',
};

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Record

Record helps you give cleaner type to objects.

Syntax

Record is written as:

Record<K, T>;

where K represents the keys and T represents the values.

Record Example

In this example, it ensures that the keys are strings and the values are numbers.

type Users = Record<string, number>;

const userRoles: Users = {
  admin: 1,
  user: 2,
  guest: 3,
};

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Exclude

Excludes from T those types that are assignable to U.

Syntax

Exclude is written as:

Exclude<T, U>;

where U represents the types you want to exclude from the union typeT.

Exclude Example

In this example, we exclude apple and banana from the union type, resulting in just orange:

type fruits = 'apple' | 'banana' | 'orange';
type ExcludedFruits = Exclude<fruits, 'apple' | 'banana'>; // "orange"

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These utility types make managing and transforming types easier, helping you write cleaner and safer code.