CODEWITHSUNDEEP
javascriptnode.js
Bas Kruithof
Bas Kruithof

Reputation: 77

Callback value returns undefined

Whenever i try to fetch the return value from a function it returns undefined.

Tried callbacks, Tried async

let express = require('express');
let fs = require('fs');
let router = express();
let mysql = require('mysql');
const session = require('express-session');

router.use(session({
    secret: 'something random.exe',
    resave: false,
    saveUninitialized: true,
    cookie: {
        expires: new Date(Date.now() + 7600000),
        maxAge: new Date(Date.now() + 7600000),
    }
}));

async function logins (username, password) {
    mysql.createQuery("SELECT * FROM Users WHERE username = ?", [username], (err, rows) => {
        return "test";
    })
}

module.exports = {
    login: async (request, response, username, password) => {
        logins("username", "password", (getResponse) => {
            return console.log(getResponse);
        })
    }
};

The console always returns undefined.

Upvotes: 0

Views: 639

Answers (2)

Neel Rathod
Neel Rathod

Reputation: 2111

It seems to be you are not aware of async/await keyword. This type of issue occurs when you try to call any function without the keyword await.

WRONG FORMAT

 const userUtils = {};

 userUtils.login = async () => {
 try {
     // Your business logic 
 } catch (err) {
     console.log(err);
     throw err;
 }
};

userUtils.test = async () => {
    try {
        const result = userUtils.login();
        console.log(result); // It will undefined
    } catch (err) {
        console.log(err);
        throw err;
    }
};

userUtils.test();

In the above code, you will get undefined as result variable.

CORRECTION

const result = await userUtils.login();

Don't forget to write a keyword await while calling any promises.

Note: You can only use async/await when you need to handle any promises. It can't work directly on callbacks

WRONG FORMAT [await while callbacks]

userUtils.test = async () => {
    try {
        const result = await userUtils.login(args, (err, data) => {
            if (err) {
                console.log(err);
                throw err;
            }
            return data;
        });
        console.log(result); // It will undefined
    } catch (err) {
        console.log(err);
        throw err;
    }
};

I hope it helps. Happy Coding :)

Upvotes: 0

Quentin
Quentin

Reputation: 943754

When you call logins you pass it three arguments:

  1. "username"
  2. "password"
  3. a function

Look at the definition of logins:

async function logins (username, password) {

It only does anything with the first two arguments.

Your callback function never gets used.

Rewrite logins to call it.

Also note that you've labeled it as async, but you aren't awaiting any promises … so that is probably a mistake.

Upvotes: 4

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