How to build a nodeJS factory?

After reading examples online on creating module and design patterns like:

http://ift.tt/1se9jxu

http://ift.tt/1xEq87A

I am not able to decide which pattern is better. At the moment, I am using a singleton pattern. Is it the correct implementation?

Essentially I want to encapsulate different modules into a factory and return an object.

Each modules has its own config.

moduleA.js

var moduleA = function(config) {
    this.wheels = config.wheels || 4;
    this.display = function() {
        console.log('wheels: '+this.wheels);
    }
};
module.exports = moduleA;

moduleB.js

var moduleB = function(config) {
    this.wheels = config.wheels || 8;
    this.display = function() {
        console.log('wheels: '+this.wheels);
    }
};
module.exports = moduleB;

factory.js

var moduleA = require('./moduleA');
var moduleB = require('./moduleB');

var factory = function(config){
    this.moduleClass = function(){};
    switch(config.type){
        case 'a' : this.moduleClass = moduleA; break;
        case 'b' : this.moduleClass = moduleB; break;
    }
    return new this.moduleClass(config);
};
module.exports = factory;

Calling it should be something like :

var config = {type:'a', wheels: 4};
var myFactory = require('./factory')(config);
myFactory.getModuleA();
config = {type:'b', wheels: 8};
myFactory.setConfig(config);