inline-es-modules.js

const files = {
  "m1.js": `import {func} from './m2.js'; console.log(func());`,
  "m2.js": `export function func() { return 'abc'; }`
}

const urls = new Map

function getURL(filename) {
  let url = urls.get(filename)
  if (!url) {
    const source = files[filename].replace(/\.\/(.+?\.m?js)/g, (_, p1) => getURL(p1))
    const blob = new Blob([ source ], { type: "text/javascript" })
    url = URL.createObjectURL(blob)
    urls.set(filename, url)
  }
  return url
}

import(getURL("m1.js"))

// https://twitter.com/rauschma/status/1171525636420063238
// https://gist.github.com/WebReflection/6a9df9477b843956f589210f8ab371c0