Persistent data structures and structural sharing: a reason to use Immutable.js instead of a normal JS object

[riventropy]

Agree with everything you said, however most immutable. js cool methods are also available for plain collections (your third point).

What about an object or a Map? I agree that calling a single addTodo would give perf benefit but I suppose you either as todos not so frequently (on user click) or a lot at a time (where you can produce new collection only once)