istype / instanceof gibberish

gistfile1.js

function log(var_) {
    console.log(var_);
    return var_;
}

function istype(test, Ctor) {
   if (Ctor == void 0 && test == void 0) return true;
   return log(test.constructor == Ctor || test instanceof Ctor);
}

istype('string', String);
istype(function(){}, Function);
istype(10, Number);
istype(false, Boolean);
istype(/regexp/, RegExp);
istype(new Date(), Date);
istype(document.createElement('div'), Element);
istype(undefined, null);
istype({}, Object);


var A = new Class({});
var b = new A();

istype(A, Class);
istype(b, A);

var C = new Class({ Extends: A });

​istype(C, Class);

​var d = new C();

​istype(d, C);
istype(d, A);​