type-fest

<div align="center"> <br> <br> <img src="media/logo.svg" alt="type-fest" height="300"> <br> <br> <b>A collection of essential TypeScript types</b> <br> <br> <br> <br> <hr> <div align="center"> <p> <p> ^{<a href="https://github.com/sponsors/sindresorhus">Sindre Sorhus' open source work is supported by the community</a>} </p> ^{Special thanks to:} <br> <br> <a href="https://standardresume.co/tech"> <img src="https://sindresorhus.com/assets/thanks/standard-resume-logo.svg" width="180"/> </a> <br> <br> <br> <a href="https://workos.com/?utm_campaign=github_repo&utm_medium=referral&utm_content=type-fest&utm_source=github"> <div> <img src="https://sindresorhus.com/assets/thanks/workos-logo-white-bg.svg" width="220" alt="WorkOS"> </div> <b>Your app, enterprise-ready.</b> <div> _{Start selling to enterprise customers with just a few lines of code.} <br> ^{Add Single Sign-On (and more) in minutes instead of months.} </div> </a> <br> <br> <br> <a href="https://transloadit.com?utm_source=sindresorhus&utm_medium=referral&utm_campaign=sponsorship&utm_content=type-fest"> <picture> <source width="350" media="(prefers-color-scheme: dark)" srcset="https://sindresorhus.com/assets/thanks/transloadit-logo-dark.svg"> <source width="350" media="(prefers-color-scheme: light)" srcset="https://sindresorhus.com/assets/thanks/transloadit-logo.svg"> <img width="350" src="https://sindresorhus.com/assets/thanks/transloadit-logo.svg" alt="Transloadit logo"> </picture> </a> <br> <br> <br> <a href="https://logto.io/?ref=sindre"> <div> <picture> <source width="200" media="(prefers-color-scheme: dark)" srcset="https://sindresorhus.com/assets/thanks/logto-logo-dark.svg?x"> <source width="200" media="(prefers-color-scheme: light)" srcset="https://sindresorhus.com/assets/thanks/logto-logo-light.svg?x"> <img width="200" src="https://sindresorhus.com/assets/thanks/logto-logo-light.svg?x" alt="Logto logo"> </picture> </div> <b>The better identity infrastructure for developers</b> <div> ^{Logto is an open-source Auth0 alternative designed for every app.} </div> </a> <br> <br> </p> </div> <br> <hr> </div> <br> <br>

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 >=5.1

Works best with {strict: true} in your tsconfig.

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.

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.
• Except - Create a type from an object type without certain keys. This is a stricter version of Omit.
• 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.
• MergeDeep - Merge two objects or two arrays/tuples recursively into a new type.
• MergeExclusive - Create a type that has mutually exclusive keys.
• OverrideProperties - Override only existing properties of the given type. Similar to Merge, but enforces that the original type has the properties you want to override.
• RequireAtLeastOne - Create a type that requires at least one of the given keys.
• RequireExactlyOne - Create a type that requires exactly a single key of the given keys and disallows more.
• RequireAllOrNone - Create a type that requires all of the given keys or none of the given keys.
• RequireOneOrNone - Create a type that requires exactly a single key of the given keys and disallows more, or none of the given keys.
• SingleKeyObject - Create a type that only accepts an object with a single key.
• RequiredDeep - Create a deeply required version of another type. Use Required<T> if you only need one level deep.
• PickDeep - Pick properties from a deeply-nested object. Use Pick<T> if you only need one level deep.
• OmitDeep - Omit properties from a deeply-nested object. Use Omit<T> if you only need one level deep.
• OmitIndexSignature - Omit any index signatures from the given object type, leaving only explicitly defined properties.
• PickIndexSignature - Pick only index signatures from the given object type, leaving out all explicitly defined properties.
• PartialDeep - Create a deeply optional version of another type. Use Partial<T> if you only need one level deep.
• PartialOnUndefinedDeep - Create a deep version of another type where all keys accepting undefined type are set to optional.
• UndefinedOnPartialDeep - Create a deep version of another type where all optional keys are set to also accept undefined.
• ReadonlyDeep - Create a deeply immutable version of an object/Map/Set/Array type. Use Readonly<T> if you only need one level deep.
• LiteralUnion - Create a union type by combining primitive types and literal types without sacrificing auto-completion in IDEs for the literal type part of the union. Workaround for Microsoft/TypeScript#29729.
• Tagged - Create a tagged type that can support multiple tags and per-tag metadata. (This replaces the previous Opaque type, which is now deprecated.)
• UnwrapTagged - Get the untagged portion of a tagged type created with Tagged. (This replaces the previous UnwrapOpaque type, which is now deprecated.)
• InvariantOf - Create an invariant type, which is a type that does not accept supertypes and subtypes.
• SetOptional - Create a type that makes the given keys optional.
• SetReadonly - Create a type that makes the given keys readonly.
• SetRequired - Create a type that makes the given keys required.
• SetNonNullable - Create a type that makes the given keys non-nullable.
• ValueOf - Create a union of the given object's values, and optionally specify which keys to get the values from.
• ConditionalKeys - Extract keys from a shape where values extend the given Condition type.
• ConditionalPick - Like Pick except it selects properties from a shape where the values extend the given Condition type.
• ConditionalPickDeep - Like ConditionalPick except that it selects the properties deeply.
• ConditionalExcept - Like Omit except it removes properties from a shape where the values extend the given Condition type.
• UnionToIntersection - Convert a union type to an intersection type.
• LiteralToPrimitive - Convert a literal type to the primitive type it belongs to.
• LiteralToPrimitiveDeep - Like LiteralToPrimitive except it converts literal types inside an object or array deeply.
• Stringified - Create a type with the keys of the given type changed to string type.
• IterableElement - Get the element type of an Iterable/AsyncIterable. For example, Array, Set, Map, generator, stream, etc.
• Entry - Create a type that represents the type of an entry of a collection.
• Entries - Create a type that represents the type of the entries of a collection.
• SetReturnType - Create a function type with a return type of your choice and the same parameters as the given function type.
• SetParameterType - Create a function that replaces some parameters with the given parameters.
• Simplify - Useful to flatten the type output to improve type hints shown in editors. And also to transform an interface into a type to aide with assignability.
• SimplifyDeep - Deeply simplifies an object type.
• Get - Get a deeply-nested property from an object using a key path, like Lodash's .get() function.
• StringKeyOf - Get keys of the given type as strings.
• Schema - Create a deep version of another object type where property values are recursively replaced into a given value type.
• Exact - Create a type that does not allow extra properties.
• OptionalKeysOf - Extract all optional keys from the given type.
• KeysOfUnion - Create a union of all keys from a given type, even those exclusive to specific union members.
• HasOptionalKeys - Create a true/false type depending on whether the given type has any optional fields.
• RequiredKeysOf - Extract all required keys from the given type.
• HasRequiredKeys - Create a true/false type depending on whether the given type has any required fields.
• ReadonlyKeysOf - Extract all readonly keys from the given type.
• HasReadonlyKeys - Create a true/false type depending on whether the given type has any readonly fields.
• WritableKeysOf - Extract all writable (non-readonly) keys from the given type.
• HasWritableKeys - Create a true/false type depending on whether the given type has any writable fields.
• Spread - Mimic the type inferred by TypeScript when merging two objects or two arrays/tuples using the spread syntax.
• IsEqual - Returns a boolean for whether the two given types are equal.
• TaggedUnion - Create a union of types that share a common discriminant property.
• IntRange - Generate a union of numbers.
• ArrayIndices - Provides valid indices for a constant array or tuple.
• ArrayValues - Provides all values for a constant array or tuple.
• ArraySplice - Creates a new array type by adding or removing elements at a specified index range in the original array.
• ArrayTail - Extracts the type of an array or tuple minus the first element.
• SetFieldType - Create a type that changes the type of the given keys.
• Paths - Generate a union of all possible paths to properties in the given object.
• SharedUnionFieldsDeep