Non-Inheritance addition of methods from a source class, either to an instance or a prototype

Mixin Decorator

/*
    @destObj    :Object to decorate
    @propName   :String name of 
    @className  :Class to use as the decorator source
*/
function decorate(destObj,propName,className)
{
    // are we working with an instance?
    if(typeof destObj == "object")
    {
        var tmp = destObj[propName] = new className();
        for(var v in tmp)
        {
            if(typeof tmp[v] == "function")
            {
                destObj[v] = function(){return tmp[v].apply(tmp,arguments);};
            }
        }
    }
    // working with prototypes
    else if(typeof destObj == "function")
    {        
        var src = className.prototype;
        var dest = destObj.prototype;
        for(var v in src)
        {
            if(typeof src[v] == "function")
            {
                dest[v] = function()
                {
                    var self = this;
                    if(!self[propName])
                    {
                        self[propName] = new className();
                    }
                    return self[propName][v].apply(self[propName],arguments);
                };
            }
        }
    }
}

// Sample Use

var MixInClass = function(){};
MixInClass.prototype.doSomething = function(blah)
{
    console.log("I am doing something with blah :: " + blah);
}

var Descendant = function(){};
var Descendant2 = function(){};

// Decorate an instance of an object with the methods of another class 
var bob = new Descendant();
decorate(bob,"_prop",MixInClass);
bob.doSomething("bob");

// Decorate a class with the methods of another class
decorate(Descendant2,"_prop",MixInClass);
var joe = new Descendant2();
joe.doSomething("joe");