How to execute the function return the value to called function across node js files

I have 3 node js files :

1. mysqlconnection.js to store the database connection properties:

   var mysql = require('mysql');
   var cjson = require('cjson');
   var yaml_config = require('node-yaml-config');
   
   // project files
   var config = yaml_config.load(__dirname + '/billingv2.yaml');
   
   
   exports.execute = function(callback){
   
       var connection = mysql.createConnection(
           {
             host     : config.host,
             user     : config.user,
             password : config.password,
             database : config.database,
           }   
       );
       connection.connect();
   
       return callback(null,connection);   
   }
   

2. subscriptionRestService.js to handle the REST api calls:

   var express = require('express');
   var app = express();
   
   app.use(express.bodyParser());
   var fs = require('fs');
   // Project files
   var mysql = require('./mysqlRestService.js');
   // Get Resource Subscription data by Resourceuri
   app.post('/pricingdetails', function(req, res) {
   
       var workload = req.body;
       if(workload.elements && workload.elements.length > 0)
       {
           var arr = [];
           for(var index in workload.elements)
           {
               arr[index] = workload.elements[index].uri;
           }
   
           var resourceIdentifiers = arr.join(',');
       }
       console.log(resourceIdentifiers);
       mysql.getPricingDetail(function(resourceIdentifiers,callback){
   
       });
   
   });
   

3. mysqlRestService.js to handle mysql queries/stored procedures:

   // packages
   var mysql = require('mysql');
   var cjson = require('cjson');
   var fs = require('fs');
   var yaml_config = require('node-yaml-config');
   
   // project files
   var dbconnection = require('./mysqlconnection');
   exports.getPricingDetail = function (resourceIdentifiers,callback){
       console.log('entered into mysql function');
       console.log(resourceIdentifiers);
       var pricingDetail = {};
       dbconnection.execute(function(err,response){
   
           if(err){
               throw err;
               }
           else 
               { 
   
                   var selectqueryString = "call SP_ExposePricingDetailforUI('" + resourceIdentifiers + "')";
                   response.query(selectqueryString, function(err,pricingDetail){
                   if(err) {   
                       throw err;          
                   }
                   else 
                   {
                       console.log(pricingDetail);
                       pricingDetail = pricingDetail;
   
                   }
                   });
               }
   
       });
   
       //console.log('printing pricing details');
       //console.log(pricingDetail);
   };
   

problems faced

1. Unable to send the variable resourceIdentifiers from subscriptionRestService to mysqlRestService.js

2. Unable to return the pricingdetail from mysqlRestService.js to calling function in subscriptionRestService.

Any guidance greatly appreciated.