Typescript param as type for nested-keys / object-path

Question

I'm investing hours now, but don't want to give up :-)

I have an object, an target-path and a callback-function (with the "target-value" from the object)

This screenshot shows my wish

• a value and
• the correct type of this :-)

Do you have any Idea if this is possible?
I need the function param targetPath inside a type, see TARGET_PATH_AS_TYPE
Here is my current sourcecode:

type DotPrefix<T extends string> = T extends '' ? '' : `.${T}`
type DotNestedKeys<T> = T extends Date | any[]
  ? ''
  : (
      T extends object
        ? {
            [K in Exclude<keyof T, symbol>]: `${K}${DotPrefix<
              DotNestedKeys<T[K]>
            >}`
          }[Exclude<keyof T, symbol>]
        : ''
    ) extends infer D
  ? Extract<D, string>
  : never

type PropType<T, Path extends string> = string extends Path
  ? unknown
  : Path extends keyof T
  ? T[Path]
  : Path extends `${infer K}.${infer R}`
  ? K extends keyof T
    ? PropType<T[K], R>
    : unknown
  : unknown

type TestType = {
  a: {
    b: Date
    c: number
    d?: string
  }
}

const myObject: TestType = {
  a: {
    b: new Date(),
    c: 12
  }
}

type MagicFunctionProps<T> = {
  sourceObj: T
  targetPath: DotNestedKeys<T>
  render: (value: PropType<T, 'a.b' /* TARGET_PATH_AS_TYPE */>) => void
}

const magicFunction = <T>({
  sourceObj,
  targetPath,
  render
}: MagicFunctionProps<T>): void => {
  render(`${sourceObj}[${targetPath}] > logic comes later` as any)
}

magicFunction<TestType>({
  sourceObj: myObject,
  targetPath: 'a.b',
  render: (value) => {
    console.log(value)
  }
})

DotNestedKeys: https://stackoverflow.com/a/68404823/8270748
PropTypes: https://github.com/microsoft/TypeScript/pull/40336

Thanks!!

Greetings crazyx13th