Singleton pattern with Browserify/CommonJS

Question

Trying to implement the singleton pattern within CommonJS modules, using Browserify. So far:

// foo.js

var instance = null;

var Foo = function(){
    if(instance){
        return instance;
    }
    this.num = 0;
    return instance = new Foo();
}

Foo.prototype.adder = function(){
    this.num++;
};

module.exports = Foo();

// main.js

var foo = require('./foo.js');
console.log(foo.num); // should be 0
foo.adder(); // should be 1
var bar = require('./foo.js');
console.log(bar.num); // like to think it'd be 1, not 0

First problem is that I get a maximum call stack exceeded error when I load the built JS file in the browser, but secondly, am I approaching this correctly? Is this possible?

Answer 1

First problem is that I get a maximum call stack exceeded error

Well, that comes from your Foo function recursively calling new Foo…

but secondly, am I approaching this correctly?

No. For singletons, you don't need a "class" with a constructor and a prototype - there will only ever be one instance. Simply create one object, most easily with a literal, and return that:

module.exports = {
    num: 0,
    adder: function(){
        this.num++;
    }
};