Typescript remove first argument from a function

Question

I have a possibly weird situation that I'm trying to model with typescript.

I have a bunch of functions with the following format

type State = { something: any }


type InitialFn = (state: State, ...args: string[]) => void

I would like to be able to create a type that represents InitialFn with the first argument removed. Something like

// this doesn't work, as F is unused, and args doesn't correspond to the previous arguments
type PostTransformationFn<F extends InitialFn> = (...args: string[]) => void

Is this possible?

Answer 1

I think you can do that in a more generic way:

type OmitFirstArg<F> = F extends (x: any, ...args: infer P) => infer R ? (...args: P) => R : never;

and then:

type PostTransformationFn<F extends InitialFn> = OmitFirstArg<F>;

PG