noThis

gistfile1.js

var splice = [].splice
  , baseClass = {
      create : function(){
        return Object.create(this)
      },
      method : function(name, fn){
        Object.defineProperty(this, name, {
          writable : true,
          configurable : true,
          enumerable : false,
          value : function(){
            splice.call(arguments, 0, 0, this)
            return fn.apply(null, arguments)
          }
        })
      }
    }

var myInstance = baseClass.create()

myInstance.method("setFoo", function(instance, value){
  instance.foo = value
})

myInstance.setFoo("bar")
myInstance.foo // "bar"