[Typescript] OverloadedReturnType & OverloadedParameters

type OverloadedReturnType<T> =
  T extends { (...args: any[]) : infer R; (...args: any[]) : infer R; (...args: any[]) : infer R ; (...args: any[]) : infer R } ? R  :
  T extends { (...args: any[]) : infer R; (...args: any[]) : infer R; (...args: any[]) : infer R } ? R  :
  T extends { (...args: any[]) : infer R; (...args: any[]) : infer R } ? R  :
  T extends (...args: any[]) => infer R ? R : any

type OverloadedParameters<T> =
  T extends { (...args: infer A1) : any; (...args: infer A2) : any; (...args: infer A3) : any ; (...args: infer A4) : any } ? A1|A2|A3|A4  :
  T extends { (...args: infer A1) : any; (...args: infer A2) : any; (...args: infer A3) : any } ? A1|A2|A3 :
  T extends { (...args: infer A1) : any; (...args: infer A2) : any } ? A1|A2  :
  T extends (...args: infer A) => any ? A : any

 

Example:

function applyChanges1(input: string): number
function applyChanges1(input: number): string
function applyChanges1(input: number | string): number | string {
  return typeof input === "number" ? input.toString() : input.length
}

function applyChanges2(input: number): string
function applyChanges2(input: string): number
function applyChanges2(input: number | string): number | string {
  return typeof input === "number" ? input.toString() : input.length
}


type OverloadedReturnType<T> = 
    T extends { (...args: any[]) : infer R; (...args: any[]) : infer R; (...args: any[]) : infer R ; (...args: any[]) : infer R } ? R  :
    T extends { (...args: any[]) : infer R; (...args: any[]) : infer R; (...args: any[]) : infer R } ? R  :
    T extends { (...args: any[]) : infer R; (...args: any[]) : infer R } ? R  :
    T extends (...args: any[]) => infer R ? R : any


type RetO1 = OverloadedReturnType<typeof applyChanges1> // string | number 
type RetO2 = OverloadedReturnType<typeof applyChanges2> // number | string

 

type OverloadedParameters<T> = 
    T extends { (...args: infer A1) : any; (...args: infer A2) : any; (...args: infer A3) : any ; (...args: infer A4) : any } ? A1|A2|A3|A4  :
    T extends { (...args: infer A1) : any; (...args: infer A2) : any; (...args: infer A3) : any } ? A1|A2|A3 :
    T extends { (...args: infer A1) : any; (...args: infer A2) : any } ? A1|A2  :
    T extends (...args: infer A) => any ? A : any


type Params01 = OverloadedParameters<typeof applyChanges1> // [string] | [number]
type Params02 = OverloadedParameters<typeof applyChanges2>  // [number] | [string]