Singleton.js

var Singleton = (function(){
  var _instance;
  function init() {
    function privateMethod() {}
    var privateVariable = "42";
    var privateRandomX = Math.random();
    return {
      publicMethod: function() {},
      publicProperty: "23",
      getRandomX: function() { return privateRandomX; }
    };
  };
  
  return {
    getInstance: function() {
      if (!_instance) {
        instance = init();
      }
      return _instance;
    }
  };
  
})();


// version 2
// static property
function Singleton() {
  if (typeof Singleton.instance === "object") {
    return Singleton.instance;
  }
  
  // init here
  
  Singleton.instance = this;  // flaw: anyone can modify
  return this;
}