Since in map we are relying on a key, that is in our case is `id`. On if deep-clone an object itself and pass it then also the lookup will not be evaluated to true. Ref:  ```  > a = {b: 'some key'};  { b: 'some key' }  > st = new WeakSet()  WeakSet { <items unknown> }  > st.add(a)  WeakSet { <items unknown> }  > st  WeakSet { <items unknown> }  > m = Object.assign({}, a)  { b: 'some key' }  > st.has(m)  false  > st.has(a)  true  >  ```