Promises JS: function response is not returned to main code

Question

I'm building a code in Node which returns a response when a promise is solved (function called: multicreation.userCreation()):

const express = require("express")
const app = express()
const csv=require('csvtojson')
const multer = require("multer")
const csvfilename = `Users-${Date.now()}.csv`
const multiUserCreation = require("./modules/fbadmin")

const multicreation = new multiUserCreation()
const upload = multer({  
     storage: storage, 
     limits: { fileSize: 1e6}
   }).single("usersdata")

app.post("/uploadCSV",function (req, res, next) { 
    upload(req,res,function(err) {   
        if(err) {   
            res.send(err) 
        } 
        else {   
            const converter=csv()
            .fromFile(`./temp/${csvfilename}`)
            .then((json)=>{
                res.send(multicreation.userCreation(json))
            })
        } 
    })
}

By the other hand, the class "multiuserCreation" code is described as below:

const admin = require("firebase-admin");
require("dotenv").config();

class multiUserCreation {
  userCreation(jsonUsers) {
    if (!admin.apps.length) {
      admin.initializeApp({
        credential: admin.credential.cert(),
        databaseURL: `https://${process.env.PROJECT_ID}.firebaseio.com/`,
      });
    }
    const db = admin.firestore();

    async function insertUsers(jsonUsers) {
      let messages = [];
      const users = jsonUsers
      for (let i = 0; i < jsonUsers.length; i++) {
        const message = await admin
          .auth()
          .createUser({
            email: jsonUsers[i]["email"],
            emailVerified: false,
            password: "password",
            disabled: false,
          })
          .then(function (userRecord) {       
            return {
              "User email": jsonUsers[i]["email"],
              Result: "Succesfully created",
            };
          })
          .catch(function (error) {
            return { "User email": jsonUsers[i]["email"], Result: error.code };
          });
        messages.push(message);
      }
      return messages;
    }

    const messageFinal = insertUsers(jsonUsers);
    messageFinal.then(function (result) {
      return messageFinal;
    });
  }
}

module.exports = multiUserCreation;

Actually, despite "messages" array is fullfiled succesffuly, multiUserCreation is not returning anything to main code. Thanks for your help

Answer 1

You need to return the promise from multicreation.userCreation Check the change below

const admin = require("firebase-admin");
require("dotenv").config();

class multiUserCreation {
  userCreation(jsonUsers) {
    if (!admin.apps.length) {
      admin.initializeApp({
        credential: admin.credential.cert(),
        databaseURL: `https://${process.env.PROJECT_ID}.firebaseio.com/`,
      });
    }
    const db = admin.firestore();

    async function insertUsers(jsonUsers) {
      let messages = [];
      const users = jsonUsers
      for (let i = 0; i < jsonUsers.length; i++) {
        const message = await admin
          .auth()
          .createUser({
            email: jsonUsers[i]["email"],
            emailVerified: false,
            password: "password",
            disabled: false,
          })
          .then(function (userRecord) {       
            return {
              "User email": jsonUsers[i]["email"],
              Result: "Succesfully created",
            };
          })
          .catch(function (error) {
            return { "User email": jsonUsers[i]["email"], Result: error.code };
          });
        messages.push(message);
      }
      return messages;
    }

    const messageFinal = insertUsers(jsonUsers);
    return messageFinal.then(function (result) {
      return messageFinal;
    });
  }
}

module.exports = multiUserCreation;

Also, while calling the userCreation, you need to handle it in a callback

  const converter=csv()
            .fromFile(`./temp/${csvfilename}`)
            .then((json)=>{
                multicreation.userCreation(json).then(function (response) {
                   res.send(multicreation.userCreation(response))
                })
            })