Fastest way to Deep Clone/Extend an object in javascript

Deep extend.js

//benchmark available here

// clone is the object to recursively copy the attributes of obj to overwriting as necessary.

function x(clone, obj) {
   for(var i in obj)
     clone[i] = (typeof obj[i] == "object") ? x(obj[i].constructor(), obj[i]) : obj[i];
   return clone;
}

or even (obj[i] && typeof obj[i] == "object")

this ends up being 3 times faster than JSON.parse(JSON.stringify(obj)) and is barely more code 😍