[acemarke]

A `===` comparison is explicitly _not_ a deep comparison. It's a reference comparison, ie, "are these two variables pointing to the same object in memory?". Under the hood, that probably is interpreted as a simple pointer comparison, which is fast and cheap. That's why it's the preferred approach for doing comparisons in cases like this. _If_ you update your data immutably, then you get the benefit of quick and simple comparisons to see if things are different.

Now, a reference comparison only tells you if the objects themselves are different. It's entirely possible to have two different objects with the same or equivalent contents, such as in @kasbah's example. Both objects have a key named `a` that has a value of 1, but the objects are different references. The overall assumption when you update data immutably and compare like this is that _if_ two objects are different references, then they _probably_ have different contents, and it's time to re-render your UI.