Returning a value from an asynchronous callback (Node.JS)

Question

So, I have my route which console.logs 'undefined':

router.get("/validate-pin", async (req, res) => {
  // restrict when done
  try {
    const { userId, pin } = req.query;
    const isActivePin = await pinsDB.compareActivePin(userId, pin);
    console.log(isActivePin)
    return res.status(200).json(isActivePin);
  } catch (error) {
    console.log(error);
    res.status(500).json({ error: "db error: ", error });
  }
});

I have my compareActivePin method, which logs out the 'res' parameter, but for some reason doesn't return it:

async function compareActivePin(userId, received_pin) {
  const active_pin = await db("account_pins").where({ userId, isActive: true });
  const pinIsValidated = bcrypt.compareSync(
    received_pin,
    active_pin[0].account_pin
  );

  if (pinIsValidated) {
    let skLocation = await db("sks").where({ userId }).select("url");
    await readKey(skLocation[0].url, (res) => {
      // console.log(res);
      return res;
    });
  } else return false;
}

And I have my readKey method, which actually grabs the data I want my compareActivePin to return. This works like a charm.

const readKey = async (key, callback) => {
  const aws = require("aws-sdk");

  aws.config.update({
    secretAccessKey: process.env.AWS_SECRET_ACCESS_KEY,
    accessKeyId: process.env.AWS_ACCESS_KEY_ID,
    region: "us-east-2",
  });

  const s3 = new aws.S3();

  const getParams = { Bucket: process.env.SK_BUCKET, Key: `${key}.txt` };

  await s3.getObject(getParams, (err, data) => {
    if (err) return err;
    return callback(data.Body.toString());
  });
};

So, just to recap. When I hit my endpoint, I pass in a userId and pin (strings). This calls the compareActivePin method which validates the pin and then, if the pin is valid, it then calls readKey, which grabs the file from S3 and returns the text within the file.

Like I said, I'm able to log it out to the console from within the readKey callback, but when I try to log it out as the returned value from the route, it comes back undefined.

Hoping someone could point me in the right direction.

Thanks...

A.Codera · Accepted Answer · 2021-09-26 22:20:57Z

I ended up answering my own question. I don't think it's possible to get a return value from the callback, so I ended up paring down the call from the database and sending the response from the readKey function using the router response object, like so:

//CompareActivePin Function

async function compareActivePin(userId, received_pin) {
  const active_pin = await db("account_pins").where({ userId, isActive: true });
  const pinIsValidated = bcrypt.compareSync(
    received_pin,
    active_pin[0].account_pin
  );
  return pinIsValidated;
}

//Router Call

router.get("/validate-pin", async (req, res) => {
  // restrict when done
  try {
    const { userId, pin } = req.query;
    const isActivePin = await pinsDB.compareActivePin(userId, pin);
    if (isActivePin) {
      let skLocation = await skDB.findUrl(userId);
      readKeyFunc(skLocation[0].url, (result) => {
        return res.status(200).json({ confirmed: isActivePin, key: result });
      });
    } else return res.status(401).json({ confirmed: isActivePin, key: null });
  } catch (error) {
    res.status(500).json({ error: "db error: ", error });
  }
});

This also goes a long way toward keeping my database methods pure and separating my concerns.

Thanks, StackOverflow!

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