Example singleton class and example for Coffeescript

singleton.coffee

class Singleton
  # We can make private variables!
  instance = null    

  # Static singleton retriever/loader
  @get: ->
    if not @instance?
      instance = new @
      instance.init()
    
    instance

  # Example class method for debugging
  init: (name = "unknown") ->
    console.log "#{name} initialized" 

class Test extends Singleton
  init: ->
    super "Test"

  run: ->
    alert "OHAI"

class OtherTest extends Singleton
  init: ->
    super "Other Test"

  run: ->
    alert "WUT"

Test.get().run()
OtherTest.get().run()
Test.get().run()

singleton.js

var OtherTest, Singleton, Test;
var __hasProp = Object.prototype.hasOwnProperty, __extends = function(child, parent) {
  for (var key in parent) { if (__hasProp.call(parent, key)) child[key] = parent[key]; }
  function ctor() { this.constructor = child; }
  ctor.prototype = parent.prototype;
  child.prototype = new ctor;
  child.__super__ = parent.prototype;
  return child;
};
Singleton = (function() {
  var instance;
  function Singleton() {}
  instance = null;
  Singleton.get = function() {
    if (!(this.instance != null)) {
      instance = new this;
      instance.init();
    }
    return instance;
  };
  Singleton.prototype.init = function(name) {
    if (name == null) {
      name = "unknown";
    }
    return console.log("" + name + " initialized");
  };
  return Singleton;
})();
Test = (function() {
  __extends(Test, Singleton);
  function Test() {
    Test.__super__.constructor.apply(this, arguments);
  }
  Test.prototype.init = function() {
    return Test.__super__.init.call(this, "Test");
  };
  Test.prototype.run = function() {
    return alert("OHAI");
  };
  return Test;
})();
OtherTest = (function() {
  __extends(OtherTest, Singleton);
  function OtherTest() {
    OtherTest.__super__.constructor.apply(this, arguments);
  }
  OtherTest.prototype.init = function() {
    return OtherTest.__super__.init.call(this, "Other Test");
  };
  OtherTest.prototype.run = function() {
    return alert("WUT");
  };
  return OtherTest;
})();
Test.get().run();
OtherTest.get().run();
Test.get().run();

This works:

 class Singleton
  @getInstance: ->
    @_instance ?= new @(@,arguments...)

  constructor: (args...) ->
    unless @constructor ==  args.shift()
      throw new Error('Cannot call new on a Singleton')
    return args


class Manager extends Singleton
  constructor: ->
    [@arg] = super

(from https://coderwall.com/p/nsyuia)