Comment by sophiebits

Still shallow.

We usually recommend avoiding deep checks because

(a) the concept of deep equality is pretty nebulous and hard to design in a predictable, precise way, and

(b) deep equality checking can be slow, often just as slow (or slower) than the actual rerender – in which case the memoization is only hurting you.

(If you want to do deep equality anyway, you can pass a second argument to React.memo to specify a custom comparator.)