Usage

StrictExtract<string | number | boolean, string>; // ^? string

Installation

CLI

npx atmx add type strict-extract

Manually

Copy and paste the following method into @/utils/helpers/undefined.ts:

import type { Any } from "@/types/any.ts";

export type SwitchAny<T, U> = [T] extends [Any] ? U : T;

export type SwitchNever<T, U> = [T] extends [never] ? U : T;

/**
* Extract types in `T` that are assignable to `U`.
* Coerce `any` and `never` types to unknown.
*
* @example
* StrictExtract<string | number | boolean, string> // ^? string
*/
export type StrictExtract<T, U> = SwitchNever<
Extract<SwitchAny<T, unknown>, U>,
unknown
>;