Can't return data from function in node js

Question

I can't return any data from function from different js file

token.js file :

var express = require('express');
var jwt = require('jsonwebtoken');
var md5 = require('md5');
var Super = require('../models/super');
var db = new Super();

var router = express.Router();

/* GET users listing. */
router.post('/Login', function(req, res) {
   var username = req.headers['username'];
   var password = req.headers['password'];
   var md5pass = md5(password);

   var ress = db.get('app_user',"username = '"+username+"' and password = '"+md5pass+"'",null,null);
   res.send(ress);
});

module.exports = router;

File super.sj :

var db = require('../config/database');
class Super{
   get(table, where, order, limit){
       if(where != null && order != null && limit != null){
        db.query('SELECT * FROM $1 WHERE $2 ORDER BY $3 LIMIT $4', [table, where, order, limit], (err, result) => {
            if(err) throw err;
            return result.rows;
        });
    }
   }
}
module.exports = Super;

on postman can'n get any data or error response

@satyampathak `db.query()` is an an async call. It has a callback. — Neil Lunn, Apr 28 '18 at 07:15
@IrfanAlviansyah Read the linked post. You don't `return result.rows` but instead you put the code that deals with this in the callback. Or learn to construct with a Promise and await the result. That's what that answer will show you. — Neil Lunn, Apr 28 '18 at 07:16

score 2 · Accepted Answer · answered Apr 28 '18 at 07:16

That's the fake class anti-pattern - you should just export a function instead. Because db.query is asynchronous, you should convert get into a Promise if you want to be able to use its result elsewhere:

var db = require('../config/database');
function get(table, where, order, limit){
  return new Promise((resolve, reject) => {
    if(where != null && order != null && limit != null){
      db.query('SELECT * FROM $1 WHERE $2 ORDER BY $3 LIMIT $4', [table, where, order, limit], (err, result) => {
        if(err) reject(err);
        resolve(result.rows);
      });
    } else reject();
  });
}
module.exports = get;

Then consume with .then (or await):

var express = require('express');
var jwt = require('jsonwebtoken');
var md5 = require('md5');
var get = require('../models/super');

var router = express.Router();

router.post('/Login', function(req, res) {
  var username = req.headers['username'];
  var password = req.headers['password'];
  var md5pass = md5(password);

  get('app_user',"username = '"+username+"' and password = '"+md5pass+"'",null,null)
    .then(ress => res.send(ress));
});

Sounds like your server is having problems - it's got nothing to do with the code. — CertainPerformance, Apr 28 '18 at 07:48

Can't return data from function in node js

1 Answers1