js_factory.js

"use strict"

var contexts = new WeakMap()
var private_for = function(key) {
  var ctx = contexts.get(key)
  if (!ctx) {
    ctx = {}
    contexts.set(key, ctx)
  }
  return ctx
}

var helperFactory2 = function() {

  var proto = {}

  proto.getHiddenProperty = function() {
    return private_for(this).hidden_property
  }

  proto.changeHiddenProperty = function(new_val) {
    private_for(this).hidden_property = new_val
  }

  var factory = {}

  factory.createHelper = function() {
    var obj = Object.create(proto)

    // set defaults
    private_for(obj).hidden_property = "hello"

    return obj
  }

  return factory
}

var factory = helperFactory2()

var helper1 = factory.createHelper()
var helper2 = factory.createHelper()

console.log(helper1.getHiddenProperty() === helper2.getHiddenProperty())

console.log("helper1", helper1.getHiddenProperty())
console.log("helper2", helper2.getHiddenProperty())

helper1.changeHiddenProperty("hi")
helper2.changeHiddenProperty("ciao")

console.log(helper1.getHiddenProperty() === helper2.getHiddenProperty())

console.log("helper1", helper1.getHiddenProperty())
console.log("helper2", helper2.getHiddenProperty())

Please do not use this approach:).