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Why MySQL connection lost in nodejs?

I am creating a facebook chatbot using node js and to store data I used MySQL Database. Currently it is working fine. But, I have a question that, should I need to close the database connection?
I tried to do it but when I close the connection then in the next attempt it is throwing an error that No SQL Connection found
Please tell me the correct way of how to close database connection and reuse it
let databaseConnection = () =>{
let conn = mysql.createConnection({
host: "",
user: "",
password: "",
database: "",
port: ""
});
conn.connect(function (error) {
if (error) {
console.log("Error when connecting to db ",error);
setTimeout(databaseConnection, 2000);
}
else {
console.log("Connected");
}
});
conn.on('error',function(err){
console.log('db error', err);
if(err.code === 'PROTOCOL_CONNECTION_LOST') {
databaseConnection();
}else{
throw err;
}
});
return conn;
}
conn = databaseConnection();
for (let i=0;i<10;i++){
query = "SELECT name FROM info where id=?";
value = i
conn.query(query,value, function (err, result, fields) {
if (err) throw err;
console.log(result);
console.log("Data Fetched Successfully.")
})
conn.end()
}

You should end your connection after the loop
for (let i=0;i<10;i++){
query = "SELECT name FROM info where id=?";
value = i
conn.query(query,value, function (err, result, fields) {
if (err) throw err;
console.log(result);
console.log("Data Fetched Successfully.")
})
}
conn.end()

Running out of processes (Flooded with sleep)

We have a server running that has 2 connections to the database, they are both created using a pool.
Example:
var connection = mysql.createPool({
host: config.mysql.host,
user: config.mysql.user,
password: config.mysql.pass,
database: config.mysql.database
});
However, there's a lot of queries we do but a pool takes care of handling/closing active connections I was told.
Now connections are just piling up and old connections are not being taken care of. Eventually we will run out of available connections and the server will go hanging.
Query function;
var query = function(query){
return new Promise(function(resolve, reject){
con.query(query, function(err, row){
if(err){
reject(err);
}
resolve(row);
});
});
}
Usage of function;
db.query('SELECT * FROM `users` WHERE `isBanned` = 0').then(function(users){
//active users
}).catch(function(err){
...
});
All connections that are being piled up are in command Sleep
Edit: merged the connections into one database pool
Main.js
var pool = mysql.createPool({
connectionLimit: 250,
host: config.mysql.host,
user: config.mysql.user,
password: config.mysql.pass,
database: config.mysql.database,
charset: 'utf8_general_ci'
});
module.exports.pool = pool;
Database.js (pretty much just for the query function)
var main = require('./server.js');
var query = function(query){
return new Promise(function(resolve, reject){
main.pool.query(query, function(err, row){
if(err){
reject(err);
}
resolve(row);
});
});
}
module.exports = {
con: main.pool,
query: query
};

Why is it showing connection not defined?

I'm trying to use connection from a connection.js file and use it in different file webFrontend.js using exports object. Now what I get on running server is:
{
"Result": "undefinedThis is result"
}
That means connection is not defined. Why is it happening? connection is working fine if getConnection is created in same (webFrontend.js) file, but the problem is when I use getConnection in same exports function in connection.js hence the connection not defined error:
Here are 2 necessary files (routes file has no problem) that explains what I'm doing:
connection.js
var mysql = require('mysql');
exports.connExport = function () {
var connectionPool = mysql.createPool({
host: 'localhost',
user: 'root',
password: '',
database: 'rockcity_followme'
});
if(connectionPool) {
connectionPool.getConnection(function (err, connection) {
if (err) {
return err;
} else {
return connection;
}
});
}else{
var abc="return error";
return abc;
}
}
webFrontend.js
var connObj=require('../Routes/connection.js');
var connection=connObj.connExport();
exports.getIndivRecords= function(req, res, next){
res.send({
Result: connection+"This is result"
});
return next();
};

No need for the .js file extension, it's automagically added for you.
The code below uses standard error-first callbacks
webFrontend.js
var connection = require('../Routes/connection');
exports.getIndivRecords = function(req, res, next){
// connection takes a standard error-first callback
connection(function(err, conn){
if (err) {
// Handle the error returned
console.log(err);
}
// The database connection is available here as conn
console.log( "Connection:" + conn);
// presumably you want to do something here
// before sending the response
res.send({
Result: conn + "This is result"
});
});
return next();
};
connection.js
var mySQL = require('mysql');
var connectionPool = mySQL.createPool({
host: 'localhost',
user: 'root',
password: '',
database: 'rockcity_followme'
});
var getConnection = function (cb) {
connectionPool.getConnection(function (err, connection) {
// pass the error to the callback
if (err) {
return cb(err);
}
cb(null, connection);
});
};
module.exports = getConnection;

First of all #Dan Nagle was right no need of .js
Second You are getting the connection undefinded because still the method doesnt returned with result.
Use promise to call your Connection.js method
Your node is single threaded async execution,
He doest wait for the method to return a result
1) Problem with your javascript is that
var connection=connObj.connExport();
in Creation stage connection was defined by javascript as undefined and as
connObj.connExport(); as still not returned with answer
it executed this function in which connection was undefined
exports.getIndivRecords= function(req, res, next){
res.send({
Result: connection+"This is result"
});
Use promise read this first so you can understand something about promise and callback if you are unable to solve than comment i will play with it.But first you try.Thanku
Understanding promises in node.js
Ok Try This I have used promise here
var connObj = require('../Routes/connection');
connObj.connExport().then(
function (connection) {
exports.getIndivRecords = function (req, res, next) {
res.send({
Result: connection + "This is result"
});
return next();
};
}).catch(function (err) {
res.status(400).send(err);
return;
});
var mysql = require('mysql');
exports.connExport = function () {
return new Promise(function (fulfill, reject) {
var connectionPool = mysql.createPool({
host: 'localhost',
user: 'root',
password: '',
database: 'rockcity_followme'
});
if (connectionPool) {
connectionPool.getConnection(function (err, connection) {
if (err) {
return reject(err);
} else {
return fulfill(connection);
}
});
} else {
var abc = "return error";
return reject(abc);
}
});
}

node js server: issue passing a variable to a function

I am building my first node.js server to perform a mysql query and return results from the database. Everything works but now I cannot find the right way to pass a value from the url (query section) to the function that performs the query (the PollingLoop function). No problems to retrieve the url and to get the parameter in the handler function but to move it to pollingLoop I have tried almost all I know about javascript (not enough I see). This is my code now that fails to run because of the reference error in pollingLoop for hwkey that is not defined.
var app = require('http').createServer(handler),
io = require('socket.io').listen(app),
url = require('url'),
fs = require('fs'),
mysql = require('mysql'),
connectionsArray = [],
connection = mysql.createConnection({
host: 'localhost',
user: 'root',
password: 'flipper',
database: 'oclock',
port: 3306
}),
POLLING_INTERVAL = 3000,
pollingTimer;
// If there is an error connecting to the database
connection.connect(function(err) {
// connected! (unless `err` is set)
if (err) {
console.log(err);
}
});
// creating the server ( localhost:8000 )
app.listen(8000);
function handler(req, res) {
console.log("INCOMING REQUEST: "+req.method+" "+req.url);
req.parsed_url = url.parse(req.url, true);
var getp = req.parsed_url.query;
var hwkey = getp.hk;
console.log(hwkey);
fs.readFile(__dirname + '/client.html', function(err, data) {
if (err) {
console.log(err);
res.writeHead(500);
return res.end('Error loading client.html');
}
res.writeHead(200);
res.end(data);
});
}
function pollingLoop(){
// Doing the database query
var query = connection.query('SELECT max(id), testo, created_by FROM flashmsgs WHERE hwk="'+hwkey+'"'),
//var query = connection.query('SELECT max(id), testo, created_by FROM flashmsgs'),
flashmsgs = []; // this array will contain the result of our db query
// setting the query listeners
query
.on('error', function(err) {
// Handle error, and 'end' event will be emitted after this as well
console.log(err);
updateSockets(err);
})
.on('result', function(flashmsg) {
// it fills our array looping on each user row inside the db
flashmsgs.push(flashmsg);
})
.on('end', function() {
// loop on itself only if there are sockets still connected
if (connectionsArray.length) {
pollingTimer = setTimeout(pollingLoop, POLLING_INTERVAL);
updateSockets({
flashmsgs: flashmsgs
});
} else {
console.log('The server timer was stopped because there are no more socket connections on the app')
}
});
};
// creating a new websocket to keep the content updated without any AJAX request
io.sockets.on('connection', function(socket) {
console.log('Number of connections:' + connectionsArray.length);
// starting the loop only if at least there is one user connected
if (!connectionsArray.length) {
pollingLoop();
}
socket.on('disconnect', function() {
var socketIndex = connectionsArray.indexOf(socket);
console.log('socketID = %s got disconnected', socketIndex);
if (~socketIndex) {
connectionsArray.splice(socketIndex, 1);
}
});
console.log('A new socket is connected!');
connectionsArray.push(socket);
});
var updateSockets = function(data) {
// adding the time of the last update
data.time = new Date();
console.log('Pushing new data to the clients connected ( connections amount = %s ) - %s', connectionsArray.length , data.time);
// sending new data to all the sockets connected
connectionsArray.forEach(function(tmpSocket) {
tmpSocket.volatile.emit('notification', data);
});
};
console.log('Please use your browser to navigate to http://localhost:8000');

just bring on hwkey variable out from handler
var hwkey;
function handler(req, res) { hwkey = ... }
pollingLoop(){console.log(hwkey);}

Undefined query function

so I'm currently using the following code to execute queries;
var mysql = require('mysql');
var config = require('./config');
var pool = mysql.createPool(config.mysql);
function query(statement){
return new Promise(function(resolve, reject){
pool.getConnection(function(err, connection) {
if(err) reject(err);
connection.query(statement, function(err, row){
connection.release();
if(err){
reject(err);
}
resolve(row);
})
});
});
}
module.exports = {
pool: pool,
query: query
};
Whenever the query function is called it results in a undefined error;
TypeError: Cannot read property 'query' of undefined
I'm quite out of ideas why this could be, this would be connection.getConnection is not returning a proper connection, would this mean my credentials are wrong in my createPool function?
config.mysql
mysql: {
host: 'localhost',
user: 'root',
password: '',
database: 'site',
connectionLimit : 10,
multipleStatements : true
}

The problem is on the following line you are passing in the query function when you should be passing in a string.
connection.query(query, function(err, row){
query in that case should be a string. But you defined query as a function (function query(){)
If you change the line to something LIKE the following this should work.
connection.query("SELECT * from Users", function(err, row){