promise gives undefined result in callback - node.js

Question

fileUpload.js
var Uploader = require('s3-image-uploader');
var express = require('express');
var config = require('./../config.js');
var Promise = require('promise');
var uploader = new Uploader({
aws: {
key: config.awsKey,
secret: config.awsSecret
},
websockets: false
});
exports.fileUpload = function(fileName) {
new Promise(function(resolve, reject) {
uploader.upload({
fileId: 'someUniqueIdentifier',
bucket: 'quflip',
source: './public/images/' + fileName,
name: fileName
},
function(data) { // success
console.log('upload success:', resolve);
resolve(data);
},
function(errMsg, errObject) { //error
reject(false);
});
});
};
logintest.js
var awsUpload = require('./../config/fileUpload.js');
var userData = function(req, res) {
console.log("true/false" + awsUpload.fileUpload(profile_image));
Here what is happening is, I am getting undefined value in console.log. So it means that callback is not passing the data. How can I pass the data effectively for further purpose

Answer 1

You need to chain to the promise with .then and do the log there. First, make sure you return the promise
return new Promise(function(resolve, reject) {
Then, you can do:
var userData = function (req, res) {
awsUpload.fileUpload(profile_image).then(data => {
console.log("true/false" + data);
});
}
If you are working in an environment that supports async/await, you can do this a bit more simply:
var userData = async function (req, res) {
console.log("true/false" + await awsUpload.fileUpload(profile_image));
};
Keep in mind that this will return a Promise.
I don't see where profile_image gets set, though.

Answer 2

If you want your function to actually return the promise then change this:
exports.fileUpload = function (fileName) {
new Promise(function(resolve, reject) {
// ...
});
};
to this:
exports.fileUpload = function (fileName) {
return new Promise(function(resolve, reject) {
// ...
});
};
Without the return statement the promise that you're creating is not going to get returned by your function.
But even then you won't be able to use it like this:
console.log("true/false" + awsUpload.fileUpload(profile_image));
You will have to use something like this:
awsUpload.fileUpload(profile_image).then(result => {
console.log("true/false" + result);
});
Or this, if you're using async/await and you're inside async function:
console.log("true/false" + await awsUpload.fileUpload(profile_image));