foo.js

export default function foo() {}

Makefile

setup:
	npm install esm
setup-old:
	npm install esm@3.0.84

run:
	ESM_DISABLE_CACHE=1 node -r esm test.js

realm.js

import foo from './foo.js';

export default function Realm() {}

test.js

import Realm from './realm.js';

function check() {
  const r = new Realm();
}

const r2 = new Realm();
const f = `${check}`;
console.log(`f is ${f}`);
// we need ${f} to cite a global "Realm" name, not something rewritten