Mixin objects in Javascript

mixin.js

Object.prototype.mixin = function(module, overwrite)
{
	for (var property in module)
	{
		if (overwrite || !this.hasOwnProperty(property))
		{
			this[property] = module[property];
		}
	}
}

var CoolGuy = {
	shades: function()
	{
		print("YEEEAHHHHHHHH!!!!!");
	}
}

// object mixin -- all new instances of Kenny get property
var Kenny = function(){};
Kenny.prototype.mixin(CoolGuy);
var kenneh = new Kenny();
kenneh.shades();
var kennbe = new Kenny();
kennbe.shades();


// instance mixin -- only this instance of Danny gets property
var Danny = function(){};
var dwitt = new Danny();
dwitt.mixin(CoolGuy);
dwitt.shades();
var weditt = new Danny();
weditt.shades(); // oops, no shades property