demo.js

/**
 * @typedef {import("./typings").Car} Car
 */

/**
 * @type {Car}
 */
const porsche993 = {};

typings.ts

declare function throttle(to: number): number;
declare function brake(to: number): number;

export type Car = {
  throttle: typeof throttle;
  brake: typeof brake;
  manufacturer: string;
  series: string;
};