TypeScript: Emulate Parameters built-in

Solution

type MyParameters<T extends (...args: any[]) => unknown> = T extends (
  ...args: infer Args
) => unknown
  ? Args
  : never
  
/* _____________ Test Cases _____________ */
import type { Equal, Expect } from '@type-challenges/utils'

// @ts-expect-error
const foo = (arg1: string, arg2: number): void => {}

// @ts-expect-error
const bar = (arg1: boolean, arg2: { a: 'A' }): void => {}

const baz = (): void => {}

type cases = [
  Expect<Equal<MyParameters<typeof foo>, [string, number]>>,
  Expect<Equal<MyParameters<typeof bar>, [boolean, { a: 'A' }]>>,
  Expect<Equal<MyParameters<typeof baz>, []>>,
]

How it works

We use the infer keyword to capture the argument types and then return them.

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