Detailed explanation of singleton pattern of JavaScript design pattern

/**
  * pre singleton mode
  * Definition: Ensure that a class has only one instance and provides a global access point to access it
  * Application: Singleton pattern is a commonly used pattern. There are some objects we often only need one.
  * For example, thread pool, global cache, window objects in the browser, etc.
  */
//--------------singleton-01-------------
/*Writing method 1*/
var Singleton = function(name){
  = name;
  = null;
};

 = function(){
 alert();
};

 = function(){
 if(!){
   = new Singleton(name);
 }
 return ;
};

var a = ("amy");
var b = ("ben");
alert(a === b);

// ------------singleton-02----------------
/*Writing method 2*/
var Singleton = function(name){
  = name;
}
 = function(){
 return ;
}

 = (function(){
 var instance = null;
 return function(name){
  if(!instance){
   instance = new Singleton(name);
  }
  return instance;
 }
})();

var a = ("amy");
var b = ("ben");
alert(a === b);

// ------------singleton03-----------
/*Writing method 3*/
var Singleton = (function(){
 var instance;
 return function(name){
  if(instance){
   return instance;
  }
   = name;
  instance = this;
 }
})();
var a = new Singleton("amy");
var b = new Singleton("ben");
alert(a === b);

//-----------------------------------------------------------------------------------------------------------------------------var getSingleton = function(fn) {
 var result;
 return function() {
  if(!result) {
   result = (this, arguments);
  }
  return result;
 }
};

var getSingletonVip = (function() {
 var instance;
 return function(fn) {
  return instance || (instance = (this, arguments));
 }
})();

var createLoginUser = function() {
 var div = ("div");
  = 'This is the login box';
 (div);
 return div;
};

var createInfoGrid = function() {
 var div = ("div");
  = 'This is the list information box';
 (div);
 return div;
};
//--Execute singleton1var createUserDiv = getSingleton(createLoginUser);
createUserDiv();
createUserDiv();

//--Execute singleton2getSingletonVip(createLoginUser);
getSingletonVip(createLoginUser);