var proto    = Object.getPrototypeOf
  , keys     = Object.keys
  , class_of = {}.toString
  , arrayp   = Array.isArray

function objp(object) {
    return class_of.call(object) == '[object Object]'
}

function copy_array(object, deep) {
    return object.map(function(value) {
        return copy(value, deep) })
}

function copy_obj(object) { var result
    result = Object.create(proto(object))
    keys(object).forEach(function(key) {
        result[key] = copy(object[key], true) })

    return result
}

function copy(object, deep) {
    return arrayp(object)?  copy_array(object, deep)
         : objp(object)?    copy_obj  (object, deep)
         : /* by value */   object
}

var x = {a:1, b:2}
var y = Object.create(x); y.c = 3;
var z = {x: x, y: y}
var a = Object.create(z);
a.list = [[1, 2], [3,[4,[5]]]]

var _ = copy(a, true)
a.list[1][0] = 4
console.log(_.list[1][0] === 3)

_ = copy(z, true)
x.a = 2
console.log(_.x.a === 1)