Import aliases with the new ES Modules (Node.js 13.6) and dotenv

app.js

import Foo from '@/modules/Foo'; // This will import `src/modules/Foo.js`
import * as Modules from '@/modules'; // This will import `src/modules/index.js`

package.json

{
  "type": "module",
  "main": "./app.js",
  "scripts": {
    "start": "node --experimental-specifier-resolution=node --loader=./resolve.js ./app.js",
    "with-dotenv": "node -r dotenv/config --experimental-specifier-resolution=node --loader=./resolve.js ./app.js dotenv_config_path=./config/${NODE_ENV}.env"
  },
  "engines": {
    "node": ">=13.6.0"
  }
}

resolve.js

import { URL, pathToFileURL } from 'url';
import fs from 'fs';

const baseURL = pathToFileURL(process.cwd()).href;

export async function resolve(s, parentModuleURL = baseURL, defaultResolve) {
  let specifier = s;

  if (specifier.indexOf('@/') === 0) {
    let path = `${process.cwd()}/src/${specifier.slice(2)}`;
    try {
      fs.statSync(path);
      // Must be a directory if no error
      path += '/index.js';
    } catch (e) {
      path += '.js';
    }
    specifier = new URL(path, parentModuleURL).href;
  }

  // Defer to Node.js for all other specifiers
  return defaultResolve(specifier, parentModuleURL, defaultResolve);
}