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

A collection of essential TypeScript types

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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

• 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

• 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

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

• TsConfigJson - Type for TypeScript's tsconfig.json file (TypeScript 3.7).

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

• Sindre Sorhus

• Jarek Radosz

• Dimitri Benin

• Pelle Wessman

License

(MIT OR CC0-1.0)

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