javascript - Node.js "Cannot read property 'prototype' of undefined" error

I am working through Brad Dayley's Node.js, MongoDB and Angularjs book and I'm stuck on one of his exercises (Listing 4.4). I have a simple script emitterListener.js that is as follows the script is designed to makes checks on an account.

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);

When I run this I get the error.

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

From my limited understanding after researching I think this means that the "on" module is not being loaded. I found a solution that suggested something similar to adding this to line 1

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

which then results in the error.

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

Following the logic from the first fix I tried implementing the same fix but with EventEmitter

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

Hooray it looks like it worked.... or not......and now I get this error

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

I tried adding the below code thinking why not?

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

and it just brings me back to the same error from before

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

What am I doing wrong here? How should I go about debugging this and where should I look? Thanks in advance for helping a newbie out.

Cheers.

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);

When I run this I get the error.

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

From my limited understanding after researching I think this means that the "on" module is not being loaded. I found a solution that suggested something similar to adding this to line 1

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

which then results in the error.

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

Following the logic from the first fix I tried implementing the same fix but with EventEmitter

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

Hooray it looks like it worked.... or not......and now I get this error

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

I tried adding the below code thinking why not?

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

and it just brings me back to the same error from before

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

What am I doing wrong here? How should I go about debugging this and where should I look? Thanks in advance for helping a newbie out.

Cheers.

Share Improve this question edited Nov 12, 2020 at 17:43 asked Aug 8, 2014 at 4:55 cwmacken 3551 gold badge3 silver badges12 bronze badges

1 If you change: 'Account.prototype._proto_ = events.EventEmitter.prototype;' to: ’Account.prototype. = Object.create(events.EventEmitter.prototype);’ does that help? Let the import as it was because adding the .on only breaks it. More info on prototype here: stackoverflow.com/questions/16063394/… – HMR Commented Aug 8, 2014 at 5:41
1 Looks like you may need.require('events').EventEmitter as well: nodejs.org/api/events.html – HMR Commented Aug 8, 2014 at 5:46

Add a comment |

6 Answers 6

Sorted by: Reset to default 8

process.EventEmitter is deprecated, use require('events') instead.

Search through all your reference files (should be in multiple files) for:

var EventEmitter = process.EventEmitter

An where ever it exists, change that line to this:

var EventEmitter = require('events')

I'll post it as an answer so this question won't get marked as unanswered.

You should change:

Account.prototype.__proto__ = events.EventEmitter.prototype;

to:

Account.prototype = Object.create(events.EventEmitter.prototype);

var EventEmitter = process.EventEmitter is deprecated in high version of node, use var EventEmitter = require('events') instead

This compilation error because of versions conflicts of npm and node. I had the same issue in my project. I resolved after install the same compatible versions of npm and node as on another machine.

Check:

nmp -v

and

node -v.

All the confusion with the actual example is the first line of code.

 var events = require('events');

After Node v6.1.0 this line of code will store EventEmmiter object inside events variable, so there is no need to access it explicitly later.

Solution is very simple, just change

events.EventEmitter.call(this);

to:

events.call(this)

And change

Account.prototype._proto_ = events.EventEmitter.prototype;

to:

Account.prototype._proto_ = events.prototype;

I had the same problem a few minutes ago, I decided to downgrade node to version 6.x, then it worked

科技改变生活-雨落星辰 - 所有的伟大,都源于一个勇敢的开始

javascript - Node.js "Cannot read property 'prototype' of undefined" error - Node.js, MongoDB

6 Answers 6

与本文相关的文章

评论列表(0)