Singleton JavaScript Pattern

Singleton pattern

// http://kaijaeger.com/articles/the-singleton-design-pattern-in-javascript.html

var Singleton = (function() {
    var instance = null;

    function PrivateConstructor() {
        var rand = Math.round(Math.random() * 100);
        this.getRand = function() {
            return rand;
        } 
    }

    return new function() {
        this.getInstance = function() {
            if (instance == null) {
                instance = new PrivateConstructor();
                instance.constructor = null;
            }
            return instance;
        }
    }
})();

var singletonInstance = Singleton.getInstance();

// =============================
// In a remotely aspect oriented kind of way, you could even do this:
// =============================

var global = this;

function singletonify(constructorName) {
    var constructorFunc = global[constructorName];
    var instance = null;

    global[constructorName] = new function() {
        this.getInstance = function() {
            if (instance == null) {
                instance = new constructorFunc();
                instance.constructor = null;
            }
            return instance;
        }
    }
}

function RegularConstructor() {
    var rand = Math.round(Math.random() * 100);
    this.getRand = function() {
        return rand;
    } 
}

singletonify("RegularConstructor");

var myInstance = RegularConstructor.getInstance();
document.write(myInstance.getRand());