Javascript: best Singleton pattern [duplicate]

Javascript: best Singleton pattern [duplicate]

Possible Duplicate:
Simplest/Cleanest way to implement singleton in JavaScript?

I’m using this pattern for singletons, in the example the singleton is PlanetEarth:
var NAMESPACE = function () {

var privateFunction1 = function () {
privateFunction2();
};

var privateFunction2 = function () {
alert(‘I\’m private!’);
};

var Constructors = {};

Constructors.PlanetEarth = function () {
privateFunction1();
privateFunction2();
};

Constructors.PlanetEarth.prototype = {
someMethod: function () {
if (console && console.log) {
console.log(‘some method’);
}
}
};

Constructors.Person = function (name, address) {
this.name = name;
this.address = address;
};

Constructors.Person.prototype = {
walk: function () {
alert(‘STOMP!’);
}
};

return {
Person: Constructors.Person, // there can be many
PlanetEarth: new Constructors.PlanetEarth() // there can only be one!
};

}();

Since PlanetEarth’s constructor remains private, there can only be one.
Now, something tells me that this self-cooked thing isn’t the best one can do, mostly because I don’t have an academic education and I tend to solve problems in stupid ways. What would you propose as a better alternative my method, where better is defined as stylistically better and/or more powerful?

Solutions/Answers:

Solution 1:

(1) UPDATE 2019: ES7 Version

class Singleton {
    static instance;

    constructor() {
        if (instance) {
            return instance;
        }

        this.instance = this;
    }

    foo() {
        // ...
    }
}

console.log(new Singleton() === new Singleton());

(2) ES6 Version

class Singleton {
    constructor() {
        const instance = this.constructor.instance;
        if (instance) {
            return instance;
        }

        this.constructor.instance = this;
    }

    foo() {
        // ...
    }
}

console.log(new Singleton() === new Singleton());

Best solution found:
http://code.google.com/p/jslibs/wiki/JavascriptTips#Singleton_pattern

function MySingletonClass () {

  if (arguments.callee._singletonInstance) {
    return arguments.callee._singletonInstance;
  }

  arguments.callee._singletonInstance = this;

  this.Foo = function () {
    // ...
  };
}

var a = new MySingletonClass();
var b = MySingletonClass();
console.log( a === b ); // prints: true

For those who want the strict version:

(function (global) {
  "use strict";
  var MySingletonClass = function () {

    if (MySingletonClass.prototype._singletonInstance) {
      return MySingletonClass.prototype._singletonInstance;
    }

    MySingletonClass.prototype._singletonInstance = this;

    this.Foo = function() {
      // ...
    };
  };

var a = new MySingletonClass();
var b = MySingletonClass();
global.result = a === b;

} (window));

console.log(result);

Solution 2:

Why use a constructor and prototyping for a single object?

The above is equivalent to:

var earth= {
    someMethod: function () {
        if (console && console.log)
            console.log('some method');                             
    }
};
privateFunction1();
privateFunction2();

return {
    Person: Constructors.Person,
    PlanetEarth: earth
};

Solution 3:

Extending the above post by Tom, if you need a class type declaration and access the singleton instance using a variable, the code below might be of help. I like this notation as the code is little self guiding.

function SingletonClass(){
    if ( arguments.callee.instance )
        return arguments.callee.instance;
    arguments.callee.instance = this;
}


SingletonClass.getInstance = function() {
    var singletonClass = new SingletonClass();
    return singletonClass;
};

To access the singleton, you would

var singleTon = SingletonClass.getInstance();

Solution 4:

function SingletonClass() 
{
    // demo variable
    var names = [];

    // instance of the singleton
    this.singletonInstance = null;

    // Get the instance of the SingletonClass
    // If there is no instance in this.singletonInstance, instanciate one
    var getInstance = function() {
        if (!this.singletonInstance) {
            // create a instance
            this.singletonInstance = createInstance();
        }

        // return the instance of the singletonClass
        return this.singletonInstance;
    }

    // function for the creation of the SingletonClass class
    var createInstance = function() {

        // public methodes
        return {
            add : function(name) {
                names.push(name);
            },
            names : function() {
                return names;
            }
        }
    }

    // wen constructed the getInstance is automaticly called and return the SingletonClass instance 
    return getInstance();
}

var obj1 = new SingletonClass();
obj1.add("Jim");
console.log(obj1.names());
// prints: ["Jim"]

var obj2 = new SingletonClass();
obj2.add("Ralph");
console.log(obj1.names());
// Ralph is added to the singleton instance and there for also acceseble by obj1
// prints: ["Jim", "Ralph"]
console.log(obj2.names());
// prints: ["Jim", "Ralph"]

obj1.add("Bart");
console.log(obj2.names());
// prints: ["Jim", "Ralph", "Bart"]