design patterns - Javascript Singleton Factory -

so i've got singleton "class" works pretty well:

function base_singleton () {     if ( base_singleton.prototype._singletoninstance )         return base_singleton.prototype._singletoninstance;     else         return base_singleton.prototype._singletoninstance = this; } 

this works great. make multiple instances if want, , reflect changes of each other:

var sing1 = new base_singleton(); var sing2 = new base_singleton(); sing1.foo = "bar"; sing2.foo === "bar"; // true 

so want able create multiple singleton interfaces, own info. i'm open way of accomplishing this. 2 methods came mind either extending or making factory.

when try extending, new object gets prototype of base_singleton, it's not extending it's creating instance.

i figure best way via factory can create new object each time:

var singleton_factory = new function () {     // let's assume in web environment     var global = global || window;       /**      * build new object singleton functionality.      * singleton functionality based https://goo.gl/yfmith      *      * idea there instance of object shared through       * singleton's prototype. can create many 'new' singletons      * desire, mirror same prototypical object.      *       * @param  {string} singletonname name of new singleton, ,       *                                prototype      * @param  {object} namespace     namespace add new object      *       * @return {object}               newly created singleton      */     this.make = function ( singletonname, namespace ) {         // default global object defined earlier         namespace = namespace || global;         // if there shared _singletoninstance, return         if ( namespace[singletonname].prototype._singletoninstance )             return namespace[singletonname].prototype._singletoninstance;         //  if there isn't one, create , return 'this'         else             return namespace[singletonname].prototype._singletoninstance = this;     } } 

problem here i'm trying use prototype on undefined.

how can create factory can create new prototype functionality of base_singleton?