CODEWITHSUNDEEP
javascriptnode.jsexpresspromise
alt-rock
alt-rock

Reputation: 357

promise returns undefined in node module.exports

The Promise returns undefined when trying to log it in routes.js, however works fine when logging in queries.js. How should i change the promise to correctly return a response to routes.js?

in queries.js:

const rsClient = require('./client.js');

const query = {
    one: 'SELECT * FROM my.db'
}

module.exports = {
    rsProdRecs: (req, res) => {
         rsClient.query(query.one)
            .then(res => {
                return res;
            })
            .catch(err => console.log(err));
    }
};

in routes.js

var express = require('express');
var router = express.Router();
var queries = require('../queries');

router.get('/', function(req, res, next) {
  const data = queries.rsProdRecs();
  console.log(data)
  res.send(data);
});

module.exports = router;

Upvotes: 0

Views: 776

Answers (2)

Jake Holzinger
Jake Holzinger

Reputation: 6063

There's a few issues with your code. The first issue has already been pointed out by other users, you need to return the promise from rsProdRecs. The then and catch blocks are also problematic as well as how you are consuming the method in your route, as described in the code below:

module.exports = {
    rsProdRecs: (req, res) => {
        return rsClient.query(query.one);

        // This is redundant, you're not transforming res in any way so this can be omitted.
        // .then(res => {
        //     return res;
        // })

        // This will cause the promise to return 'undefined' if rsClient.query(...) rejects,
        // instead error handling should be done in the calling function.
        // .catch(err => console.log(err));
    }
};

And you can refactor your route to properly consume your Promise returning method:

router.get('/', function (req, res, next) {
    // We cannot consume the "data" directly, we must wait for the promise to resolve.
    queries.rsProdRecs()
        .then((data) => {
            console.log(data);
            res.send(data);
        })
        .catch((err) => {
            console.log(err);
            res.status(500); // insert correct error response here
        });

});

Or use async/await since you are already using ES6 funcionality:

router.get('/', async function (req, res, next) {
    try {
        const data = await queries.rsProdRecs();
        console.log(data);
        res.send(data);
    } catch (e) {
        console.log(err);
        res.status(500);
    }
});

Upvotes: 2

Andry Shutka
Andry Shutka

Reputation: 413

Did you try add return statement?

rsProdRecs: (req, res) => {
         return rsClient.query(query.one)
            .then(res => {
                return res;
            })
            .catch(err => console.log(err));
    }

Upvotes: 2

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