Js.Obj
val empty : unit -> < .. > t
val assign : < .. > t -> < .. > t -> < .. > t
val merge : < .. > t -> < .. > t -> < .. > t
merge obj1 obj2 assigns the properties in obj2 to a copy of obj1. The function returns a new object, and both arguments are not mutated
merge obj1 obj2
obj2
obj1
val keys : _ t -> string array