async function* paginate(items, pageSize) {
  for (let i = 0; i < items.length; i += pageSize) {
    const page = items.slice(i, i + pageSize);
    yield await Promise.resolve(page);
  }
}

async function* transform(source, fn) {
  for await (const chunk of source) {
    yield fn(chunk);
  }
}

async function run() {
  const data = [10, 20, 30, 40, 50, 60];

  const pages = paginate(data, 2);
  const mapped = transform(pages, (page) => page.map((x) => x * 2));

  const results = [];
  for await (const page of mapped) {
    results.push(page.reduce((a, b) => a + b, 0));
  }

  console.log(results);
}

run();