const fs = require('fs').promises;

const IDFILE = `id.txt`;

async function* generator() {
  let id;
  try {
    const data = await fs.readFile(IDFILE);
    id = parseInt(data.toString());
  } catch (error) {
    id = 0;
  }

  while (true) {
    id++;
    await fs.writeFile(IDFILE, id.toString());

    yield id;
  }
}

(async () => {
  const idGenerator = generator();
  let id = await idGenerator.next();
  console.log(id.value);
  id = await idGenerator.next();
  console.log(id.value);
  id = await idGenerator.next();
  console.log(id.value);
  id = await idGenerator.next();
  console.log(id.value);
})();