How a express to pass object to other file? - node.js

Question

In app.js, when express running, express will create pool connection. then pool instance can be access in other file. How to do that?
app.js
const express = require('express');
const app = express();
const port = 8080;
const mysql = require('mysql2');
const comic = require('./routes/comic');
app.use('/comics', comic);
app.listen(port, () => {
console.log(`Server is listening in ${port} port`);
const pool = mysql.createPool({
host:'localhost',
user: 'root',
password: 'test',
database: 'test'
});
exports.connection = pool.promise();
});
test.js
const {connection} = require('./app');
(async () => {
const [rows] = await connection.execute('SELECT * FROM people');
console.log(rows);
})();

Answer 1

I would recommend you to have a seperate db.js file that would have the connection pool and import that pool wherever necessary
In db.js
const mysql = require('mysql2');
const pool = mysql.createPool({
host:'localhost',
user: 'root',
password: 'test',
database: 'test'
});
module.exports = pool;
And in the place where u want it
let pool = require('./db');
const queryRes = (query, pool) => new Promise((resolve, reject) => {
pool.getConnection(function(err, connection) {
if(err) {
reject('Error');
}
connection.query(query, (err, results, fields) => {
if(err) {
reject('Error');
}
else{
connection.release();
resolve(results);
}
});
connection.on('error', (err) => {
reject('Error');
connection.release();
});
});
});
queryRes("Select * from test", pool).then(result => {
console.log(result);
}).catch(err => {
console.log(err);
});