type-fest

Many of the types here should have been built-in. You can help by suggesting some of them to the TypeScript project.

Either add this package as a dependency or copy-paste the needed types. No credit required. 👌

PR welcome for additional commonly needed types and docs improvements. Read the contributing guidelines first.

Help wanted with reviewing proposals and pull requests.

Install

npm install type-fest

Requires TypeScript >=5.9, ESM, and {strict: true} in your tsconfig.

[!NOTE] This readme shows the current development version. For docs about the latest version, see the npm page.

You may also like my ts-extras package which provides runtime functions for some of these types.

Usage

import type {Except} from 'type-fest';

type Foo = {
	unicorn: string;
	rainbow: boolean;
};

type FooWithoutRainbow = Except<Foo, 'rainbow'>;
//=> {unicorn: string}

API

Click the type names for complete docs.

Basic

• Primitive - Matches any primitive value.
• Class - Matches a class.
• Constructor - Matches a class constructor.
• AbstractClass - Matches an abstract class.
• AbstractConstructor - Matches an abstract class constructor.
• TypedArray - Matches any typed array, like Uint8Array or Float64Array.
• ObservableLike - Matches a value that is like an Observable.
• LowercaseLetter - Matches any lowercase letter in the basic Latin alphabet (a-z).
• UppercaseLetter - Matches any uppercase letter in the basic Latin alphabet (A-Z).
• DigitCharacter - Matches any digit as a string ('0'-'9').
• Alphanumeric - Matches any lowercase letter (a-z), uppercase letter (A-Z), or digit ('0'-'9') in the basic Latin alphabet.

Utilities

• EmptyObject - Represents a strictly empty plain object, the {} value.
• NonEmptyObject - Represents an object with at least 1 non-optional key.
• UnknownRecord - Represents an object with unknown value. You probably want this instead of {}.
• UnknownArray - Represents an array with unknown value.
• UnknownMap - Represents a map with unknown key and value.
• UnknownSet - Represents a set with unknown value.
• Except - Create a type from an object type without certain keys.
• Writable - Create a type that strips readonly from the given type. Inverse of Readonly<T>.
• WritableDeep - Create a deeply mutable version of an object/ReadonlyMap/ReadonlySet/ReadonlyArray type. The inverse of ReadonlyDeep<T>. Use Writable<T> if you only need one level deep.
• Merge - Merge two types into a new type. Keys of the second type overrides keys of the first type.
• ObjectMerge - Merge two object types into a new object type, where keys from the second override keys from the first.
• MergeDeep - Merge two objects or two arrays/tuples recursively into a new type.
• MergeExclusive - Create a type that has mutually exclusive keys.
• - Override existing properties of the given type. Similar to , but enforces that the original type has the properties you want to override.