Get variable out from function which is calling export.modules node.js

Question

In the file users.js I want to get code out of randomCode() to assign to the result and use it in whole endpoint '/login'.

randomCode.js

const crypto = require('crypto')

const randomCode = (callback) =>{
    crypto.randomInt(100000, 999999, (err, n) => {
        if (err) throw err;
        callback(n);
    });
}
    
module.exports = randomCode

users.js

require('dotenv').config()
const express = require('express')
const router = express.Router()
const randomCode = require('../controllers/randomCode')


router.get('/login', async (req, res, next)=>{
    try{
//-----------------------------------------------------
        randomCode((code) => {
          console.log(code,'code')
        })
//-----------------------------------------------------
        return res.send('ok')
    }
    catch(error){
        res.send(error)
    }
})

module.exports = router;

I tried to use await but whithout results.

router.get('/login', async (req, res, next)=>{
    try{
//------------------------------------------------------
        const result = await randomCode((code) => {
          console.log(code,'code')
        })
        console.log(result)
//------------------------------------------------------
        return res.send('ok')
    }
    catch(error){
        res.send(error)
    }
})

Why don't you just use randomCode as a helper method instead of a controller? crypto.randomInt won't ever throw an error, so you can skip the callback, just returning the code and using it like this: const code = randomCode(); However, I don't really see a problem with your code, what is the console printing? — maxpsz
– maxpsz, Commented Jan 15, 2022 at 19:25
The reason why I insert randomCode() in controller is: to find out :) I faced before with this kind of "problem" but usually I skipped it and moved function from controller to other location. — Tytus Bomba
– Tytus Bomba, Commented Jan 15, 2022 at 20:55
That's completely fair, good on you! I tried replicating that in a javascript file, and both functions seems to be working ok, so the problem must be somewhere else. What is the console.log printing your case? — maxpsz
– maxpsz, Commented Jan 15, 2022 at 21:41
Example app listening at localhost:8000-------- Database connected.------ undefined-------- 568350 code — Tytus Bomba
– Tytus Bomba, Commented Jan 15, 2022 at 21:50

kca · Accepted Answer · 2022-01-15 22:48:41Z

There would be different approaches (especially as crypto.randomInt could be called synchronously), but I understand you are specifically interested in how to get a value from an asynchronous function, so I'll answer that:

const randomCode = function(){
  return new Promise((resolve, reject) => {
    crypto.randomInt(100000, 999999, (err, n) => {
      if( err ){
        reject( err );
      } else {
        resolve( n );
      }
    });
  });
}

router.get('/login', async (req, res, next)=>{
  try{
    const code = await randomCode();
    console.log(code)
    return res.send('ok')
  }
  catch(error){
    res.send(error)
  }
})

In cases where you can not change the randomCode() function for some reason, you need to wrap it into a Promise, like:

const randomCodePromise = function(){
    return new Promise((resolve, reject) => {
        randomCode((code) => {
            resolve( code );
        })
    });
}

(and obviously then use await randomCodePromise() instead of await randomCode())

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