Love this! Just wanted to note that I think there’s a mistake on the flyweight pattern page’s example. You’re using getting a boolean with Set.has but treating it like a Book (as if you had used Set.get). I also don’t really understand how this saves memory if you’re spreading the result into a new object, but maybe someone here can enlighten me!

Ah I think I understand now. The return type of createBook is true | Book, which is likely a mistake, but happens to work because when you attempt to spread a boolean into an object it removes itself. But if you were to edit the example to have a stable return type of Book then it would no longer save memory, so perhaps that was intentional?