如何修复返回`undefined`的异步函数？

Question

I'm trying to return the count from my database. The count().exec method returns a Promise. I'm trying to resolve it in order to return the value to the user. But it returns undefined .

It seems to me I have well used the async/await pattern, so what is wrong? I can't figure it out.

Here my snippet :

app.get("/blog/page/:pageTargeted", (req, res) => {
  var countQuery = Posts.estimatedDocumentCount().exec();

  // estimate count of document in collecion 
  function estimation() {
    countQuery.then(count => {
      countStringified = count.toString();
      return countStringified;
    })
  } // console.log => successfully returns a value

  // set Data
  async function setData() {
    let countStringified = await estimation();
    return countStringified;
  }

  // send Data
  function sendData() {
    setData().then(result => console.log("result in sendData: ", result));
  } // undefined
  sendData();
});

*** Edit *** : it's now works, here's my new snippet:

setData().then(result => { // call an async/await functions chain
  console.log("count in Post.find: ", result);
  console.log("pageTargeted in Post.find: ", pageTargeted);

  if (err) return console.error(err);
  res.status(200).send(result);
});

I'm just wondering if I have to wrap all the ulterior process inside my function call. So maybe some refactoring will occur if possible to avoid some hell-type process. Anyway, meanwhile it works, so great, thanks.

Answer 1

Your estimation() function returns undefined instead of returning a promise, that is because you return the new string from the callback function.

replace countQuery.then(...) with return countQuery.then(...) .