Typesafe path function as an alternative to safe navigation operator

path.ts

// Need to use this special type so that keyof would work
export type TheType<T> = Required<NonNullable<T>>

export function path<P extends keyof TheType<T>, T>(
  props: [P],
  obj: T
): PropType<P, T>

export function path<
  P extends keyof TheType<T>,
  P2 extends keyof TheType<T>[P],
  T
>(props: [P, P2], obj: T): PropType2<P, P2, T>

export function path<
  P extends keyof TheType<T>,
  P2 extends keyof TheType<T>[P],
  P3 extends keyof Required<TheType<T>[P]>[P2],
  T
>(props: [P, P2, P3], obj: T): PropType3<P, P2, P3, T>

export function path<
  P extends keyof TheType<T>,
  P2 extends keyof TheType<T>[P],
  P3 extends keyof Required<TheType<T>[P]>[P2],
  P4 extends keyof Required<Required<TheType<T>[P]>[P2]>[P3],
  T
>(props: [P, P2, P3, P4], obj: T): PropType4<P, P2, P3, P4, T>

export function path<
  P extends keyof TheType<T>,
  P2 extends keyof TheType<T>[P],
  P3 extends keyof Required<TheType<T>[P]>[P2],
  P4 extends keyof Required<Required<TheType<T>[P]>[P2]>[P3],
  T
>(props: [P] | [P, P2] | [P, P2, P3] | [P, P2, P3, P4], obj: T): any {
  if (obj === null || obj === undefined) {
    return obj
  }

  const [prop, ...tail] = props
  const value = (obj as any)[prop]

  if (value === null || value === undefined) {
    return value
  }

  if (props.length === 1) {
    return value
  }

  return path(tail as any, value)
}

export type PropType<P extends keyof TheType<T>, T> = undefined extends T
  ? TheType<T>[P] | undefined
  : TheType<T>[P]

export type PropType2<
  P extends keyof TheType<T>,
  P2 extends keyof TheType<T>[P],
  T
> = TheType<T>[P] extends object
  ? undefined extends T
    ? PropType<P2, TheType<T>[P]> | undefined
    : PropType<P2, TheType<T>[P]>
  : never

export type PropType3<
  P extends keyof TheType<T>,
  P2 extends keyof TheType<T>[P],
  P3 extends keyof Required<TheType<T>[P]>[P2],
  T
> = TheType<T>[P] extends object
  ? undefined extends T
    ? PropType2<P2, P3, TheType<T>[P]> | undefined
    : PropType2<P2, P3, TheType<T>[P]>
  : never

export type PropType4<
  P extends keyof TheType<T>,
  P2 extends keyof TheType<T>[P],
  P3 extends keyof Required<TheType<T>[P]>[P2],
  P4 extends keyof Required<Required<TheType<T>[P]>[P2]>[P3],
  T
> = TheType<T>[P] extends object
  ? undefined extends T
    ? PropType3<P2, P3, P4, TheType<T>[P]> | undefined
    : PropType3<P2, P3, P4, TheType<T>[P]>
  : never