Extract Type

index.ts

// @see https://stackoverflow.com/questions/60449479/typescript-extract-type-from-object-by-object-path-in-tuple

type ExtractType<O, T extends Array<any>> = {
  [K in keyof O]: ((...a: T) => any) extends (a: any, ...args: infer Tail) => any
    ? Tail['length'] extends 0
      ? O[K]
      : ExtractType<O[K], Tail>
    : never
}[T[0]]

// example Foo is number
type Foo = ExtractType<{ a: { b: { c: { d: number } } }; g: string }, ['a', 'b', 'c', 'd']>