Node.js 无法在NodeJs中要求类？

我有两个文件：

mysqlDAOFactory.js:

var mysql = require('mysql');
var mysqlUserDAO = require('./mysqlUserDAO');
var mysqlSessionDAO = require('./mysqlSessionDAO');


class mysqlDAOFactory {

    static createConnection() {
        var connection = mysql.createConnection({
            host:'localhost',
            user:'root',
            password:'',
            database:'QASys'
        });
        return connection;
    }

    static getDbInstance() {
        return mysql;
    }

    getUserDAO() {
        return new mysqlUserDAO();
    }
    getSessionDAO() {
        return new mysqlSessionDAO();
    }
}

module.exports = mysqlDAOFactory;

var mysqlDAOFactory = require('./mysqlDAOFactory.js');
var bcrypt = require('bcryptjs');
var preparedStatements = require('./preparedStatements');

class mysqlUserDAO {
    constructor() {
        this.connection = mysqlDAOFactory.createConnection();
        this.mysql = mysqlDAOFactory.getDbInstance();
    }
}

module.exports = mysqlUserDAO;

var mysqlDAOFactory = require('./mysqlDAOFactory.js');
var UserDAO = mysqlDAOFactory.getUserDAO();

mysqlUserDAO.js:

var mysql = require('mysql');
var mysqlUserDAO = require('./mysqlUserDAO');
var mysqlSessionDAO = require('./mysqlSessionDAO');


class mysqlDAOFactory {

    static createConnection() {
        var connection = mysql.createConnection({
            host:'localhost',
            user:'root',
            password:'',
            database:'QASys'
        });
        return connection;
    }

    static getDbInstance() {
        return mysql;
    }

    getUserDAO() {
        return new mysqlUserDAO();
    }
    getSessionDAO() {
        return new mysqlSessionDAO();
    }
}

module.exports = mysqlDAOFactory;

var mysqlDAOFactory = require('./mysqlDAOFactory.js');
var bcrypt = require('bcryptjs');
var preparedStatements = require('./preparedStatements');

class mysqlUserDAO {
    constructor() {
        this.connection = mysqlDAOFactory.createConnection();
        this.mysql = mysqlDAOFactory.getDbInstance();
    }
}

module.exports = mysqlUserDAO;

var mysqlDAOFactory = require('./mysqlDAOFactory.js');
var UserDAO = mysqlDAOFactory.getUserDAO();

当我运行文件test.js:

var mysql = require('mysql');
var mysqlUserDAO = require('./mysqlUserDAO');
var mysqlSessionDAO = require('./mysqlSessionDAO');


class mysqlDAOFactory {

    static createConnection() {
        var connection = mysql.createConnection({
            host:'localhost',
            user:'root',
            password:'',
            database:'QASys'
        });
        return connection;
    }

    static getDbInstance() {
        return mysql;
    }

    getUserDAO() {
        return new mysqlUserDAO();
    }
    getSessionDAO() {
        return new mysqlSessionDAO();
    }
}

module.exports = mysqlDAOFactory;

var mysqlDAOFactory = require('./mysqlDAOFactory.js');
var bcrypt = require('bcryptjs');
var preparedStatements = require('./preparedStatements');

class mysqlUserDAO {
    constructor() {
        this.connection = mysqlDAOFactory.createConnection();
        this.mysql = mysqlDAOFactory.getDbInstance();
    }
}

module.exports = mysqlUserDAO;

var mysqlDAOFactory = require('./mysqlDAOFactory.js');
var UserDAO = mysqlDAOFactory.getUserDAO();

程序无法识别mysqlUserDAO.js中类的构造函数中的变量mysqlDAOFactory，尽管我以前需要这个变量。 有人能解释一下为什么会发生这种事吗

---

我已经检查了您的cod，您犯了循环依赖的错误，因为您没有运行代码

我对mysqlSession文件有临时注释，因为您没有发布MySQL会话文件

请参阅正在运行的示例，然后也请查看链接。

test.js：

mysqlUserDAO.js

mysqlDAOFactory.js

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我觉得这条路不对。你能检查一下吗？路径是正确的，因为我已经在构造函数中分配了变量（var mysqlDAOFactory=require（'./mysqlDAOFactory.js'），它可以工作。但我想知道为什么我把它放在外面时它不起作用。@SnapeSeverus@SnapeSeverus请检查代码，让我知道它对您是否起作用？@SnapeSeverus请检查我的答案很高兴帮助您，让我知道它是否能解决您的问题，如果不能，那么仍然可以帮助您找到解决方案？