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.

Install

$ npm install type-fest

Requires TypeScript >=3.2

Usage

import {Omit} from 'type-fest';

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

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

API

Click the type names for complete docs.

Basic

• Primitive - Matches any primitive value.
• Class - Matches a class constructor.
• TypedArray - Matches any typed array, like Uint8Array or Float64Array.
• JsonObject - Matches a JSON object.
• JsonArray - Matches a JSON array.
• JsonValue - Matches any valid JSON value.
• ObservableLike - Matches a value that is like an Observable.

Utilities

• Omit - Create a type from an object type without certain keys.
• Mutable - Convert an object with readonly properties into a mutable object. Inverse of Readonly<T>.
• Merge - Merge two types into a new type. Keys of the second type overrides keys of the first type.
• MergeExclusive - Create a type that has mutually exclusive properties.
• RequireAtLeastOne - Create a type that requires at least one of the given properties.
• ReadonlyDeep - Create a deeply immutable version of a object/Map/Set/Array type.
• 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.

Miscellaneous

• PackageJson - Type for npm's package.json file.

Declined types

If we decline a type addition, we will make sure to document the better solution here.

• Diff and Spread - The PR author didn't provide any real-world use-cases and the PR went stale. If you think this type is useful, provide some real-world use-cases and we might reconsider.

Tips

Built-in types

There are many advanced types most users don't know about.

• Partial<T> - Make all properties in T optional.
• Required<T> - Make all properties in T required.
• Readonly<T> - Make all properties in T readonly.
• Pick<T, K> - From T, pick a set of properties whose keys are in the union K.
• Record<K, T> - Construct a type with a set of properties K of type T.
• Exclude<T, U> - Exclude from T those types that are assignable to U.
• Extract<T, U> - Extract from T those types that are assignable to U.
• NonNullable<T> - Exclude null and undefined from T.
• Parameters<T> - Obtain the parameters of a function type in a tuple.
• ConstructorParameters<T> - Obtain the parameters of a constructor function type in a tuple.
• ReturnType<T> – Obtain the return type of a function type.
• InstanceType<T> – Obtain the instance type of a constructor function type.

You can find some examples in the TypeScript docs.

Maintainers

• Sindre Sorhus
• Jarek Radosz
• Dimitri Benin

License

(MIT OR CC0-1.0)