Why is the value of this returned promise not updating?

Question

I have a program where, upon clicking a button, the "likes" attribute of a randomly fetched MongoDB document is supposed to update. However, it does not. I am able to call the fetched document through the button, not not actually update it:

MongoClient.connect(DBconnection, { useUnifiedTopology: true })
  .then(client => {
    const db = client.db(database);
    const collection = db.collection(table);

    //R has been previously defined as a random number
    let doc = function(data) {
      return db.collection(table).find().limit(-1).skip(R - 1).next()
        .then(results => { return results })
    }
    
    //This is supposed to update the value of the randomly fetched document
    app.post("/", (req, res) => {
      let w = doc()
      w.then(function(results) {
        console.log(results) //This correctly returns the random document
      })
      //This line is meant to update document "w", but it does not.
      db.collection(table).updateOne({ w }, { $set: { likes: "clicked" + R } })
        .then(result => {
          res.redirect("/")
        })
        .catch(error => console.error(error))
    });
  });

The button in the ejs file is as simple as:

<form action="/" method="POST">
    <button id="updoot" type="submit">upvote</button>
</form>

Answer 1

Check the status of the promise by console logging (result). If it returns a pending promise, try async-await which will resolve the promise, and then executes res.redirect .

app.post("/", async (req, res) => {
      let w = await doc()
      const updatedData = await db.collection(table).updateOne({ w }, { $set: { likes: "clicked" + R } })
      res.redirect("/")
  });

I think it should work.

Answer 2

Alright, thanks to the contribution of jkalandarov, I was able to solve it just by adding one extra step: requesting the ObjectId of w and using that as a filter instead of the returned promise of w:

app.post("/", async (req, res) => {
      let w = await doc()
      var oid = w._id
      let updatedData = await db.collection(table).updateOne({"_id":ObjectId(oid)}, { $set: { likes: "clicked" + R } })

      res.redirect("/")
  });