Node.JS未定义不是所需模块的功能 [英] Node.JS undefined is not a function on required module

问题描述

我正在尝试使用一个我创建的名为user.js.该用户的代码是：

I'm trying to use a class that I created called user.js. The code for this user is:

function User(){};

User.prototype.addUser = function(){
    //Do stuff
    return 0;
};

module.exports = User;

我将其包含在我的index.js路由文件中，如下所示：

I'm including it in my index.js route file, which looks like this:

var config = require('../lib/config');
var db = require('../lib/db');
var User = require('../lib/user');
var express = require('express');
var router = express.Router();
var bodyParser = require('body-parser');

/* GET home page. */
router.get('/', function(req, res, next) {
    res.render('index', { title: 'Express' });
});

/* GET create user. */
router.get('/newuser', function(req, res, next) {
    *****var newuser = User.addUser();*****

    res.render('index', {   
                        user: newuser
                    });
});

module.exports = router;

但是，当我访问localhost / newuser时，我收到以下错误： TypeError：undefined不是函数。这个错误被抛出在我上面标有5个星号的行中的index.js中。

However, when I visit localhost/newuser, I get the following error: TypeError: undefined is not a function. This error is being thrown in index.js on the line I marked with 5 asterisks above.

推荐答案

您正在定义一个名为 User（）并导出它。但是，当您 require（'../ lib / user'）时，您会得到构造函数，但是您不会使用它来构造一个新对象，所以不要实际上有一个类型为 User 的对象，你只需要构造函数，因此没有方法 addUser（）构造函数。

You are defining a constructor named User() and exporting it. But, then when you require('../lib/user'), you get the constructor function, but you never construct a new object with it so you don't actually have an object of type User, you just have the constructor and thus there is no method addUser() on the constructor.

而不是这样：

var User = require('../lib/user');

您可以像这样调用构造函数：

you can call the constructor function like this:

var u = require('../lib/user');
var User = new u();

或者，如果您不需要再创建另一个，您可以一行完成所有操作： / p>

Or, if you never need to make another one, you can do it all in one line:

var User = new (require('../lib/user'))();

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