main.ts

// for instance, this TS function

import fetch from "node-fetch";

const getData = async (url: string): Promise<any | null> => {
  try {
    const response = await fetch(url);
    const json = await response.json();
    return json;
  } catch (error) {
    console.log(error);
    return null;
  }
};

// gets compiled to the following JS

"use strict";
var __importDefault = (this && this.__importDefault) || function (mod) {
    return (mod && mod.__esModule) ? mod : { "default": mod };
};
Object.defineProperty(exports, "__esModule", { value: true });
const node_fetch_1 = __importDefault(require("node-fetch"));

const getData = async (url) => {
    try {
        const response = await node_fetch_1.default(url);
        const json = await response.json();
        return json;
    }
    catch (error) {
        console.log(error);
        return null;
    }
};

// with the following tsconfig:
{
  "compilerOptions": {
    "target": "ES2020",                          
    "module": "CommonJS",                    
    "lib": ["ES2020"],                     
    "allowJs": true,
    "outDir": "build",                          
    "rootDir": "src",
    "strict": true,         
    "noImplicitAny": true,
    "esModuleInterop": true,
    "resolveJsonModule": true
  }
}