JAEGIS-METHOD-v1.0\node_modules\type-fest\readme

type-fest A collection of essential TypeScript types

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 >=3.4

Usage

import {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

Utilities

  • Except - Create a type from an object type without certain keys. This is a stricter version of Omit.

  • Mutable - Convert an object with readonly keys into a mutable object. The 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 keys.

  • 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.

  • PartialDeep - Create a deeply optional version of another type. Use Partial<T> if you only need one level deep.

  • 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.

  • Promisable - Create a type that represents either the value or the value wrapped in PromiseLike.

  • Opaque - Create an opaque type.

  • SetOptional - Create a type that makes the given keys optional.

  • SetRequired - Create a type that makes the given keys required.

  • ValueOf - Create a union of the given object's values, and optionally specify which keys to get the values from.

  • PromiseValue - Returns the type that is wrapped inside a Promise.

  • AsyncReturnType - Unwrap the return type of a function that returns a Promise.

  • 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.

  • 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.

  • Stringified - Create a type with the keys of the given type changed to string type.

  • FixedLengthArray - Create a type that represents an array of the given type and length.

  • IterableElement - Get the element type of an Iterable/AsyncIterable. For example, an array or a generator.

  • 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.

  • Asyncify - Create an async version of the given function type.

Template literal types

Note: These require TypeScript 4.1 or newer.

  • CamelCase – Convert a string literal to camel-case (fooBar).

  • KebabCase – Convert a string literal to kebab-case (foo-bar).

  • PascalCase – Converts a string literal to pascal-case (FooBar)

  • SnakeCase – Convert a string literal to snake-case (foo_bar).

  • DelimiterCase – Convert a string literal to a custom string delimiter casing.

Miscellaneous

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.

  • Dictionary - You only save a few characters (Dictionary<number> vs Record<string, number>) from Record, which is more flexible and well-known. Also, you shouldn't use an object as a dictionary. We have Map in JavaScript now.

  • SubType - The type is powerful, but lacks good use-cases and is prone to misuse.

  • ExtractProperties and ExtractMethods - The types violate the single responsibility principle. Instead, refine your types into more granular type hierarchies.

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.

  • Omit<T, K> – Constructs a type by picking all properties from T and then removing K.

You can find some examples in the TypeScript docs.

Maintainers

License

(MIT OR CC0-1.0)

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