Base and Core are good libraries, but I wouldn’t recommend them (if anybody cared to ask me 
)
Do you send the beginner in question straight to base without ever using the standard library? Then it means you are teaching them dependency management in OCaml before they are allowed to read a file.
Are you teaching them the standard library first before moving them to JS libs? It means you have to teach them 2 ways to create a Map.
I think using incompatible libs, is just too much upfront for a newcomer, and they would be much better served by starting with the standard library, and then moving to containers.