Passing variable from one js to another js file in nodejs

Question

I'm just getting started with Nodejs, so please bear with me

I store my DB setting on the first JS, connect.js :

var mysql = require('mysql');

module.exports = function(connectDB) {
  var connectDB = {};

  connectDB.connection = mysql.createConnection({
    //db params
  });

  connectDB.connection.connect(function(err) {
    if (err) {
      console.error('error connecting: ' + err.stack);
      return;
    }

    console.log('connected as id ' + connection.threadId);
  });

return connectDB;
};

Then I stored my query in another JS file, lets call it dbManager.js :

var db = require('./connect')(connectDB);

var test_connection = connectDB.connection.query('SELECT * FROM `test`', function (error, results, fields) {
  console.log(results);
});

exports.test = test_connection;

My goal is to pass the connection variable from connect.js to dbManager.js , so I could use it for running some queries.

The above code return an error, which said the variable is not passed successfully to dbManager.js :

ReferenceError: connectDB is not defined

Thanks in advance

Answer 1

The syntax error is because you cant define variables within an object literal using var .

eg, you can't do the following,

var t = {
    "r": 4,
    var g = 5;
};

You can do this,

var t = {
    "r": 4,
    "g" : 5
};

And to access the properties of the object you can do,

console.log(t["r"]);
console.log(t.g);

In your code the problem is declaring a variable inside an object literal. Yo could do,

var connectDB = {};
connectDB.connection = mysql.createConnection({
  //DB params
});
connectDB.connection.connect(function(err) {
  if (err) {
    console.error('error connecting: ' + err.stack);
    return;
  }

  console.log('connected as id ' + connectDB.connection.threadId);
});

return connectDB;

Edit1 As per OP's comments,

connect.js:- Changes- No need of the connectDB param, using module.exports functionality.

  var mysql = require('mysql');
  var connectDB = {};

  connectDB.connection = mysql.createConnection({
    //db params
  });

  connectDB.connection.connect(function(err) {
    if (err) {
      console.error('error connecting: ' + err.stack);
      return;
    }

    console.log('connected as id ' + connectDB.connection.threadId);
  });

module.exports = connectDB;

dbManager.js:-

var db = require('./connect');//removed the parameter
//use db variable to process queries as returned from the above require statement.
var test_connection = db.connection.query('SELECT * FROM `test`', function (error, results, fields) {
  console.log(results);
});

exports.test = test_connection;

Answer 2

         **you can do it like this
            connection.js**


         var mysql=require('mysql');
         // Database Connection
         var connection = mysql.createConnection({
              host     : hostname,
              user     :username,
              password : password,
              database : databasename,
              multipleStatements:true
         });
         try {
                connection.connect();

             } catch(e) {
                  console.log('Database Connetion failed:' + e);
                    }

       module.exports=connection;


       **you can use this connection file in your dbmanager file like 
         this..**

         var db = require('./connection.js');var test_connection = 
               connection.query('SELECT * FROM test', function(err,result) { 
                         console.log(result);
                   });

Answer 3

Will something like this work for you? You can have a file that returns a connection object from the pool:

var mysql = require('mysql');

module.exports = function() {
    var dbConfig = {...};
    var database = mysql.createPool(dbConfig);

    return {
        getConnection: function(callback) {
            // callback(error, connection)
            database.getConnection(callback);
        }
    };
};

Wherever you need to use it, you can require it as follows:

var connector = require('./db-connector')();

Then use it like this:

connector.getConnection(function(error, connection) {
    // Some code...

    // Be sure to release the connection once you're done
    connection.release();
});

Answer 4

This is how I store config data to pass around on my node server. I call it config.js and .gitignore it. I keep a sample copy called config.sample.js

let config = {};
config.mysql-host='localhost' || process.env.MYSQL_HOST;
config.mysql-user='me' || process.env.MYSQL_USER;
config.mysql-secret='secret' || process.env.MYSQL_SECRET;
config.mysql-database='my_db' || process.env.MYSQL_DB;
module.exports = config; //important you don't have access to config without this line.

To use it I would do the following.

const config = require('./config');
const mysql = require('mysql');

const connection = mysql.createConnection({
host: config.host,
user: config.user,
password: config.password,

});

connection.connect((err) => {
  if(err) {
  console.error(`error connecting: ${err.stack});
  return;
  }
  console.log(`connected`);
});

const test_connection = connectDB.connection.query('SELECT * FROM `test`'(error, results, fields) => {
  console.log(results);
});