Javascript 如何分别创建DBconnection和Node.js查询文件

我有个问题。如何连接dbconnection.js和demo_api_select.js我在demo_api_select.js上声明变量时遇到问题。它不工作，并且有如下错误通知：

请帮忙

dbconnection.js：

demo_api_select.js

我想让这些代码与此代码一起工作：

var mysql = require('mysql');

var con = mysql.createConnection({
  host: "localhost",
  user: "root",
  password: "",
  database: "test"
});

con.connect(function(err) {
  if (err) throw err;
  //Select all customers and return the result object:
  con.query("SELECT * FROM profil" , function (err, result, fields) {
    if (err) throw err;
    console.log(result);
  });
});

---

请尝试此代码。无需连接两次数据库

var db = require('./dbconnection');

db.query("SELECT * FROM profil" , function (err, result, fields) {
   if (err) throw err;
    console.log(result);
   });
});

---

哇，很好，谢谢

var mysql = require('mysql');

var con = mysql.createConnection({
  host: "localhost",
  user: "root",
  password: "",
  database: "test"
});

con.connect(function(err) {
  if (err) throw err;
  //Select all customers and return the result object:
  con.query("SELECT * FROM profil" , function (err, result, fields) {
    if (err) throw err;
    console.log(result);
  });
});

var db = require('./dbconnection');

db.query("SELECT * FROM profil" , function (err, result, fields) {
   if (err) throw err;
    console.log(result);
   });
});