Why is the value not returned?

Question

JavaScript

When going to the page, an array of users should be returned, but undefined comes up, which indicates the absence of the value of result , but if you call console.log(), then the value of result is there. I can't figure out what's wrong.

app.get('/users', (req, res) => {
  res.send(findOne() + "  one");
});

var findOne = (queryObj) => {
  let promise = new Promise((resolve, reject) => {
    db.collection('users').find(
      queryObj
    ).toArray((err, docs) => {
      if (!err) {
        resolve(docs);
      } else {
        reject();
      };
    })
  });
  promise.then(result => {
    return result;
  }, reject => {
    return 'error';
  });
};

Thank you!

Answer 1

try return new Promise at the beginning of writing

Answer 2

Because the value of the arrow function is returned in the promise, the findOne function itself does not return anything.
It should be like this:

app.get('/users', (req, res) => {
  findOne().then((result) => {
      res.send(result);
    })
    .catch((e) => {
      res.status(500, {
        error: e
      });
    });
});

const findOne = (queryObj) => {
  return new Promise((resolve, reject) => {
    db.collection('users').find(
      queryObj
    ).toArray((err, docs) => {
      if (!err) {
        resolve(docs);
      } else {
        reject(err);
      };
    });
  });
};