Create new instance from singleton

Question

Intro:

I have some legacy code that creates a singleton:

define(['backbone', 'MyModel'], function (Backbone, MyModel) {

  var MyCollection = Backbone.Collection.extend({
    model: MyModel,
    initialize: function () {
      //...
    }
  });

  return new MyCollection();
});

And for test purposes I need to generate new instances to inject them as dependeces.

Question:

Is there any way to generate new instances of the singleton without modifying the original code?

What I've done:

I came with a solution: add the class as a property of the instace

    initialize: function () {
      this.ClassObject = MyCollection;
      //...
    }

and then instantiate it

var myCollection = require('myCollection');
var myCollectionInstance = new myCollection.ClassObject();

This solution modifies the class and I'd like to avoid it.

I also tryed creating a copy of the singleton:

function generateNewCollection() {
  var F = function () {};
  F.prototype = myCollection;
  return new F();
}

It generates a new instance but it doesn't create new instances of its dependences, so the environment is still dirty for the next tests.

Answer 1

The solution: use the constructor function from the prototype.

var newMyCollection = new (Object.getPrototypeOf(myCollection).constructor);