yes indeed you can use the prototype object:

Date.prototype.myFunc = function () { alert('test') }

However this is a bad practice and should be avoided. Better approach, in my opinion, is to inherit the Date object:

var myDate = function() {
	this.myFunc = function() { alert('test') };
}

myDate.prototype = new Date();

var d = new myDate();

d.myFunc();

Is it possible to add a function to the super class.

I want to add a function to Date object, I don’t want to use prototype.