Extends the Class native.

• Online Tutorial/Demo

Extends a class back onto itself preserving any properties assigned to the class's namespace.

OriginalClass = Class.refactor(OriginalClass, newProperties)

1. OriginalClass - (class) the original class to augment
2. newProperties - (object) properties to assign to the class

• object - the original class with the new properties assigned. Any properties attached to the original's namespace are preserved.

MooTools is designed to be extended and as you can see in this repository, I make judicious use of that design. One of the cooler things you can do is extend a class onto itself. Let's consider the following code:

var Test = new Class({
    log: function(msg){
        console.log(msg);
    },
    msgs: {
        foo: 'bar',
        something: 'something else'
    },
    logMsg: function(msg){
        this.log(this.msgs[msg]);
    }
});
var firstTest = new Test();
firstTest.log('this is the first test instance');
firstTest.logMsg('foo'); //bar

var Test = new Class({
    Extends: Test, //extends itself!
    log: function(msg){
        this.previous(msg); //methods have reference to previous state via this.previous
        console.log('altered version of Test just logged message');
    },
    msgs: {
        foo: 'not bar anymore!' //can overwrite nested properties w/o altering others
    }
})

//firstTest is unaltered because it was instantiated perviously:
firstTest.log('this is the first test instance');
firstTest.logMsg('foo'); //bar

//but new instances get the new properties:
var secondTest = new Test();
secondTest.log('this is the second test instance'); //logs the message and
        //then "altered version..." message
secondTest.logMsg('foo'); //logs "not bar anymore!" and then "altered version.." message

If, say, you only want to change the defaults for Fx.Tween but want the Element.tween method to use those changes, then you should just use .implement. But if you want to reference the previous version of methods (similar to this.parent when you use Extends), you'll need to use refactor.