export var to routes files expressjs - node.js

Question

I'm completely new to nodejs + expressjs comming from php and I'm getting trouble how to export/include a var to my routes/users.js file.
on app.js I have:
//database connection
var connection = mysql.createConnection({
host : 'localhost',
user : 'root',
password : '',
database : 'dbNodeExpress'
});
... some code
var user = require('./routes/user'); //here I include my routes/files (I dont know if it's right to include the routes here - for learning purposes it works for now)
... more code until starts the server
On my /routes/user.js
app = require('../app');
//var mysql = require('mysql');
var baseUrl = app.get('baseUrl');
app.get('/users_mysql', function(req, res){
connection.query('SELECT * FROM users', function(err, users){
res.json(users);
});
});
and I get the express error: 500 ReferenceError: connection is not defined
The connection works because if I move the content from users.js to app.js I can query the database.
My questions is how to inject the var connection to be used on routes/users.js
Any help / hint to understand this is very appreciated. Thanks in advance.

Answer 1

There are several ways you could do this. A couple solutions might be:
Create a resources.js file that creates and exports the connection. Then require() resources.js in every source file where you need it.
Pass the connection to your user route file. Something like this:
// app.js
var connection = mysql.createConnection({
host : 'localhost',
user : 'root',
password : '',
database : 'dbNodeExpress'
});
require('./routes/user')(connection);
// routes/user.js
module.exports = function(connection) {
app.get('/users_mysql', function(req, res){
connection.query('SELECT * FROM users', function(err, users){
res.json(users);
});
});
};

Answer 2

create a database connector javascript file. as like database_connector.js
and require it when ever you want to have the connection pooled or the connection class availabel to your models. tip : you can also export config files like below or use barely values.
var mysql = require('mysql');
var config = require("./config");
function Connection() {
this.pool = null;
this.init = function() {
this.pool = mysql.createPool({
connectionLimit: config.poolSize,
host: config.host,
user: config.user,
password: config.password,
database: config.database,
debug:config.debug,
});
};
this.acquire = function(callback) {
this.pool.getConnection(function(err, connection) {
callback(err, connection);
});
};
console.log("connection"+this.pool);
}
module.exports = new Connection();