MySql command is work from terminal but is not working from node js

Question

I have a strange problem in my nodejs website. I have a function to execute an SQL command. It works perfectly but after running server for a few days. It start to return an empty array!!! And when I restart the server it back to work again but still crashing after few days.

This is the error (the empty array error) :

TypeError: Cannot read property '0' of undefined
    at Query._callback (/home/mikro/www/my_modules/database.js:47:27)
    at Query.Sequence.end (/home/mikro/www/node_modules/mysql/lib/protocol/sequences/Sequence.js:86:24)
    at /home/mikro/www/node_modules/mysql/lib/protocol/Protocol.js:226:14
    at _combinedTickCallback (internal/process/next_tick.js:73:7)
    at process._tickDomainCallback (internal/process/next_tick.js:128:9)

and this is the function :

login: function (username, password, callback) { 
        db.query('SELECT id, password, expdate FROM users WHERE username=' +
            mysql.escape(username) + ';', function (err, rows) {
            var row = rows[0];
            if (err) console.error(err)
            if (!row)
                callback(ERR_USER_NOT_FOUND, null);
            else
            bcrypt.compare(password, row.password, function (err, result) {
                if (result){
                    var expdate = row.expdate;
                    var currDate = moment(new Date()).format('YYYY-MM-DD HH:mm:ss');
                    if (moment(currDate).isAfter(expdate) && row.id !== 1)
                        callback ('Please pay your monthly fee to be able to login', null);
                    else
                        callback(null, row)
                }
                else {
                    callback(ERR_WRONG_PASSWORD, null);
                }
            })
        });
    }

I have Ubuntu server and run pm2 with nginx proxy. my dependencies :

"dependencies": {
    "bcrypt-nodejs": "latest",
    "body-parser": "~1.16.0",
    "connect-flash": "^0.1.1",
    "cookie-parser": "~1.4.3",
    "debug": "~2.6.0",
    "ejs": "~2.5.5",
    "express": "~4.14.1",
    "express-session": "^1.15.1",
    "moment": "^2.18.1",
    "morgan": "~1.7.0",
    "mysql": "latest",
    "serve-favicon": "~2.3.2",
    "socket.io": "latest",
    "jwt-simple": "latest",
    "jsonfile": "latest",
    "express-mysql-session": "latest",
    "express-rate-limit": "latest"
  }

---

Update1

This is the connection code :

var mysql  = require('mysql');
var db     = mysql.createConnection(require('./config'));
db.connect();

Answer 1

if I understood the issue correctly, it might be an issue of MySQl connection reset due to network timeout, or connection Idle time out.

better check the error at MySql connection code.

e.g. One of MySql connection issue logged at : nodejs mysql Error: Connection lost The server closed the connection