javascript - Node.js "Cannot read property ' 原型(prototype)“未定义”错误 - Node.js、MongoDB 和 Angularjs 书

Question

我正在阅读 Brad Dayley 的 Node.js、MongoDB 和 Angularjs 一书，但我一直坚持他的一项练习( list 4.4)。我有一个简单的脚本emitterListener.js，如下所示，该脚本旨在对帐户进行检查。

var events = require('events');
function Account() {
    this.balance = 0;
    events.EventEmitter.call(this);
    this.deposit = function(amount) {
        this.balance += amount;
        this.emit('balanceChanged');
    };
    this.withdraw = function(amount) {
        this.balance -= amount;
        this.emit('balanceChanged');
    };
}
Account.prototype._proto_ = events.EventEmitter.prototype;

function displayBalance() {
    console.log("Account balance: $%d", this.balance);
}

function checkOverdraw() {
    if (this.balance < 0) {
        console.log("Account Overdrawn!!!!!");
    }
}

function checkGoal(acc, goal) {
    if (acc.balance > goal) {
        console.log("Goal Achieved!!!!!");
    }
}
var account = new Account();

account.on("balanceChanged", displayBalance);
account.on("balanceChanged", checkOverdraw);
account.on("balanceChanged", function() {
    checkGoal(this, 1000);
});
account.deposit(220);
account.deposit(320);
account.deposit(600);
account.withdraw(1200);

当我运行它时，我得到了错误。

TypeError: Object #<Account> has no method 'on'
at Object.<anonymous> (/Users/506132/web/emitterListener.js:35:9)
at Module._compile (module.js:456:26)
at Object.Module._extensions..js (module.js:474:10)
at Module.load (module.js:356:32)
at Function.Module._load (module.js:312:12)
at Function.Module.runMain (module.js:497:10)
at startup (node.js:119:16)
at node.js:906:3

根据我在研究后的有限理解，我认为这意味着“on”模块没有被加载。我找到了一个建议类似于将其添加到第 1 行的解决方案

var events = require('events').on;

然后导致错误。

TypeError: Cannot read property 'EventEmitter' of undefined
at Object.<anonymous> (/Users/506132/web/emitterListener.js:16:35)
at Module._compile (module.js:456:26)
at Object.Module._extensions..js (module.js:474:10)
at Module.load (module.js:356:32)
at Function.Module._load (module.js:312:12)
at Function.Module.runMain (module.js:497:10)
at startup (node.js:119:16)
at node.js:906:3

按照第一个修复的逻辑，我尝试使用 EventEmitter 实现相同的修复

var events = require('events').EventEmitter;

万岁，它看起来像它工作......或者没有......现在我得到这个错误

TypeError: Cannot read property 'prototype' of undefined
at Object.<anonymous> (/Users/506132/web/emitterListener.js:17:48)
at Module._compile (module.js:456:26)
at Object.Module._extensions..js (module.js:474:10)
at Module.load (module.js:356:32)
at Function.Module._load (module.js:312:12)
at Function.Module.runMain (module.js:497:10)
at startup (node.js:119:16)
at node.js:906:3

我尝试添加下面的代码，为什么不呢？

var events = require('events').prototype;

它只是让我回到以前的相同错误

TypeError: Cannot read property 'EventEmitter' of undefined
at Object.<anonymous> (/Users/506132/web/emitterListener.js:16:35)
at Module._compile (module.js:456:26)
at Object.Module._extensions..js (module.js:474:10)
at Module.load (module.js:356:32)
at Function.Module._load (module.js:312:12)
at Function.Module.runMain (module.js:497:10)
at startup (node.js:119:16)
at node.js:906:3

我在这里做错了什么？我应该如何去调试这个，我应该去哪里看？提前感谢您帮助新手。

干杯。

Answer 1

process.EventEmitter 已弃用，请改用 require('events')。

在您的所有引用文件(应该在多个文件中)搜索:

var EventEmitter = process.EventEmitter

无论它存在于何处，将该行更改为:

var EventEmitter = require('events')