// await 回传必须是一个aysnc function 且返回必须是promise.
async function sleep(key, delay) {
  return new Promise(function (resolve, reject) {
    setTimeout(function () {
      resolve({
        key: key,
        delay: delay
      });
    }, delay);
  })
}

router.get('/',  async (ctx) => {
  let list = {};
  let list.a = await sleep('a', 100);
  let list.b = await sleep('b', 100);
  let list.c = await sleep('c', 100);
  let list.d = await sleep('d', 100);
  return ctx.body = list;
});