[WorldMaker]

JS allows numbers as object keys (though it's one of those weird behavioral swamps where arrays act differently from objects, and sometimes they are coerced to strings [objects] and sometimes not [arrays], depending), so this mostly seems that its just about getting better at defining the existing JS behaviors of things, modulo the "quirks" of course.

A lot of this matters in "metaprogramming" like Readonly<T> and Partial<T> which use all of the existing keys in a type to produce a "new" result (none of the key can be set, and all of the keys are optional, respectively), and making sure it doesn't miss intentional keys like symbols and numbers.