How do I properly create prototype objects from another file in Node.js?

Question

I'm running into a really frustrating problem in Node.js.

I'll start with what I'm doing.

I'm creating an object in a file and then exporting the constructor and creating it in other files.

My objects are defined like so:

File 1:

var Parent = function() {};

Parent.prototype = {
     C: function () { ... }
}

module.exports = Parent;

File 2:

var Parent = require('foo.js'),
      util = require('util'),
      Obj = function(){ this.bar = 'bar' };
util.inherits(Obj, Parent);
Obj.prototype.A = function(){ ... };
Obj.prototype.B = function(){ ... };
module.exports = Obj;

I'm trying to use the object like so in another file

File 3:

var Obj = require('../obj.js'),
      obj = new Obj();

obj.A();

I receive the error:

TypeError: Object [object Object] has no method 'A'

however when I run Object.getPrototypeOf(obj) I get:

{ A: [Function], B: [Function] }

I have no idea what I'm doing wrong here, any help would be appreciated.

What does util.inherits do? Does your code work if you omit the Parent thing (since A is a Obj-method)? — Bergi
– Bergi, Commented Feb 3, 2013 at 23:51
I'm not able to help you, i will come back if I find a solution. — vault
– vault, Commented Feb 4, 2013 at 0:48
It's worth noting that, in addition to my answer, if I copy and paste your source code, above (and fix the path issues and replace the ...s), I can run it with no issues. — Michelle Tilley
– Michelle Tilley, Commented Feb 4, 2013 at 0:52

Michelle Tilley · Accepted Answer · 2013-02-04 00:56:03Z

5

I cannot reproduce your problem. Here is my setup:

parent.js

var Parent = function() {};

Parent.prototype = {
  C: function() {
    console.log('Parent#C');
  }
};

module.exports = Parent;

child.js

var Parent = require('./parent'),
    util = require('util');

var Child = function() {
  this.child = 'child';
};

util.inherits(Child, Parent);

Child.prototype.A = function() {
  console.log('Child#A');
};

module.exports = Child;

main.js

var Child = require('./child');
child = new Child();

child.A();
child.C();

And running main.js:

$ node main.js
Child#A
Parent#C

The source code is clonable via Git at the following Gist: https://gist.github.com/4704412

Aside: to clarify the exports vs module.exports discussion:

If you want to attach new properties to the exports object, you can use exports. If you want to completely reassign exports to a new value, you muse use module.exports. For example:

// correct
exports.myFunc = function() { ... };
// also correct
module.exports.myFunc = function() { ... };

// not correct
exports = function() { ... };
// correct
module.exports = function() { ... };

edited Feb 4, 2013 at 0:56

answered Feb 4, 2013 at 0:42

Michelle Tilley

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7 Comments

CalvinR Over a year ago

Thanks for the info I'm afraid there might be something else wrong that I'm doing. I'll check out your example on my setup.

CalvinR Over a year ago

Okay I must be doing something else wrong since your code works fine in my environment.

CalvinR Over a year ago

what method do you use for what I'm trying to do?

Michelle Tilley Over a year ago

@CalvinR I don't understand. What are you trying to do? I replicated your code in my answer, and it works. There must be a problem elsewhere. If you can explain your issue, I'd be happy to try to help.

CalvinR Over a year ago

turns out I know what I'm doing, I just don't know how to spell my problem was a case mismatch in what I was calling my function and how I was calling it, get vs Get :(

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