function Test() { this.child = {}; }
var obj = new Test(); // provided a normal js object, which
obj.child.obj = obj; // can contain cycles
obj.child2 = obj.child // and references

var cow = new Cow(obj);
var proxy = cow.proxy;

// the proxy has all the properties of obj!
proxy.child.obj === proxy;
proxy.child2 === proxy.child;

// we can write new properties
proxy.child3 = proxy; // even create new cycles!

// convert the proxy back to plain object:
var finished = cow.finish();
finished.child3 === finished;
finished.child.obj === finished;
finished.child === finished.child2;

// and it has left the original object untouched:
obj !== finished;
obj.child !== finished.child;