This is a misunderstanding of how Arrays work. When you have an object with exactly two keys, it is very fast to iterate through them.

So what this code demonstrates is that if you have to look up a billion keys, that is going to be slower than if you have to look up two keys for an object.

Additional reading for this: https://v8.dev/blog/fast-properties From this article:

const sparseArray = []; sparseArray[9999] = 'foo'; // Creates an array with dictionary elements. In this example, allocating a full array with 10k entries would be rather wasteful. What happens instead is that V8 creates a dictionary where we store a key-value-descriptor triplets. The key in this case would be '9999' and the value 'foo' and the default descriptor is used. Given that we don't have a way to store descriptor details on the HiddenClass, V8 resorts to slow elements whenever you define an indexed properties with a custom descriptor: