Importing/exporting Typescript type definitions in Node.js worker threads

Question

I am learning Typescript and ran into the following problem with Node.js worker threads:

In a tutorial I found this JS code to be implemented by the worker:

//worker.js
const {parentPort} = require("worker_threads");

parentPort.on("message", data => {
  parentPort.postMessage({num: data.num, fib: getFib(data.num)});
});

function getFib(num) {
  if (num === 0) {
    return 0;
  }
  else if (num === 1) {
    return 1;
  }
  else {
    return getFib(num - 1) + getFib(num - 2);
  }
}

... together with this parent thread:

//app.js

const {Worker} = require("worker_threads");

//Create new worker
const worker = new Worker("./worker.js");

//Listen for a message from worker
worker.on("message", result => {
  console.log(`${result.num}th Fibonacci Number: ${result.fib}`);
});

worker.on("error", error => {
  console.log(error);
});

worker.postMessage({num: 40});
worker.postMessage({num: 12});

As an exercise I wanted to transfer this into Typescript. When I want to implement this

//types.ts

type CalcValue = {
  num: number;
  fib: number;
}

... the following seems to work fine

//app.js

import {CalcValue} from "./types";

const {Worker} = require("worker_threads");

//Create new worker
const worker = new Worker("./worker.js");

//Listen for a message from worker
worker.on("message", (result: CalcValue) => {
  console.log(`${result.num}th Fibonacci Number: ${result.fib}`);
});

worker.on("error", (error: any) => {
  console.log(error);
});

... but when I want to add the same typing in the worker file, I get error messages.

//worker.ts

import {CalcValue} from "./types";

const {parentPort} = require("worker_threads");

parentPort.on("message", (data: CalcValue) => {
  parentPort.postMessage({num: data.num, fib: getFib(data.num)});
});

function getFib(num: number): number {
  if (num === 0) {
    return 0;
  }
  else if (num === 1) {
    return 1;
  }
  else {
    return getFib(num - 1) + getFib(num - 2);
  }
}

[1] import CalcValue from "./types";
[1] ^^^^^^
[1] 
[1] SyntaxError: Cannot use import statement outside a module

How would I solve this?