Java Script Promises

Question

What I am trying to do:

This HTTP call updates the password in the database. I send the new password to go get hashed and salted in getHashedPassword(), and this works, at least according to the console.log where a hash number is printed.

Problem: body data-field does not get updated when I reassign it with the result from the promise, proven by the console log right outside the promise. So thus in the database the new literal string password gets updated but not hash. I'll provide output and pictures in case my explaining is confusing.

    router.put('/:id', (req, res) => {
        
          getHashedPassword(req.body.password01).then( result => {
            console.log('this is the hashed', result);
            req.body.password01 = result;
          })
          console.log('new passwords', req.body.password01);
          BasicUser.findByIdAndUpdate(req.params.id, req.body)
            .then(user => res.json({ msg: 'Updated successfully' }))
            .catch(err =>
              res.status(400).json({ error: 'Unable to update the Database' })
            );
        
        });

Console.logs:

new passwords helloagain339
this is the hashed $2b$10$fPw/bHW69mnyltWh0Qn3T.hKIsxbhgTt8/OGxOQXVVRDpTICqZCy.

The handler function is completely synchronous, so OFC you'll see the "new password" log before the asynchronous code completes and logs "this is the ...". Convert the handler to be `async` and then `await` all the asynchronous logic instead of using Promise chains. — Drew Reese, Nov 04 '21 at 05:26
@notacoder check my answer below. I've shown the approaches you can follow to get this issue resolved. Please upvote & accept the answer if you find it helpfull, so that it may help other who stumble upon it in future. — Salvino D'sa, Nov 04 '21 at 05:36
"*this is the hashed*" appearing **after** the "*new passwords*" in the console should give away what's happening — Bergi, Nov 04 '21 at 05:47

score 2 · Answer 1 · answered Nov 04 '21 at 05:26

Okay, the issue is that BasicUser.findByIdAndUpdate runs before the getHashedPassword promise can resolve and return the response so that it can be passed on to findByIdAndUpdate. The way to solve it is use async/await or put second promise within the callback of the first one.

Async / Await approach

router.put("/:id", async (req, res) => {
  try {
    req.body.password01 = await getHashedPassword(req.body.password01);
    console.log("new passwords", req.body.password01);
    const user = await BasicUser.findByIdAndUpdate(req.params.id, req.body);
    res.json({ msg: "Updated successfully" });
  } catch (error) {
    res.status(400).json({ error: "Unable to update the Database" });
  }
});

Nested callback approach

router.put("/:id", (req, res) => {
  getHashedPassword(req.body.password01).then((result) => {
    console.log("this is the hashed", result);
    req.body.password01 = result;
    console.log("new passwords", req.body.password01);
    BasicUser.findByIdAndUpdate(req.params.id, req.body)
      .then((user) => res.json({ msg: "Updated successfully" }))
      .catch((err) =>
        res.status(400).json({ error: "Unable to update the Database" })
      );
  });
});

P.S: I would recommend the async-await approach

score 1 · Answer 2 · edited Nov 04 '21 at 05:32

You can use async/await to make code more readable like this

router.put('/:id', async (req, res) => {
  let result = await getHashedPassword(req.body.password);
  req.body.password01 = result;
  console.log('new passwords', req.body.password01);
  BasicUser.findByIdAndUpdate(req.params.id, req.body)
    .then(user => res.json({ msg: 'Updated successfully' }))
    .catch(err => res.status(400).json({ error: 'Unable to update the Database' }));
});

Java Script Promises

2 Answers2

Async / Await approach

Nested callback approach

P.S: I would recommend the async-await approach