Ah, Javascript ...

gistfile1.js

> l = require('lodash');
> cloneFoo = l.clone(foo)
{ one: 1, two: 2 }
> delete cloneFoo['one']
true
> cloneFoo
{ two: 2 }
> foo
{ one: 1, two: 2 }
> var changer = function(d) {
... copy = l.clone(d);
... delete copy['one'];
... }
> changer(foo)
> foo
{ one: 1, two: 2 }
> foo2 = {}
{}
> foo2.test = {  one : 1 }
{ one: 1 }
> foo2
{ test: { one: 1 } }
> var changer2 = function(d) { 
... d2 = l.clone(d);
... delete d2.test['one'];
... }
> changer2(foo2)
> foo2
{ test: {} }