[BUG] Using two Js_of_ocaml compiled libraries in the same runtime causes issues with js stubs

[troederjs]

Describe the bug
If two separate ocaml libraries have JS stubs which define the same symbol ion joo_global_object (e.g. two different versions of src-bindings/node/dune in the OCaml VSCode extension) they will conflict when both libraries are loaded by different Js_of_ocaml executable.

This happens because joo_global_object is the globalThis, and so the two values override each other.

Normally, when running a single application this is not a problem since we can control all the dependencies and ensure they don't conflict. But specifically in the case of the VSCode extension, this causes issues when there are two Js_of_ocaml extensions that use incompatible versions of the nodejs binding stubs.

Expected behavior
Both Js_of_ocaml executable should be able to run independently in the same JS environment.

[hhugo]

First note that joo_global_object should be avoided, support will be removed at some point. One should use globalThis instead.

It seems to me that vscode-ocaml-platform is part of the problem here. It should not update the global object,it should defined its own stubs.

[troederjs]

What is the correct way to access a JS stub without making it available on some global context like globalThis?

[hhugo]

https://ocsigen.org/js_of_ocaml/latest/manual/linker gives some information.

In short,

//Provides: customAdd
function customAdd(a,b){
  return a + b
}

 external add : int -> int -> int = "customAdd"

[hhugo]

I've worked on a bunch of changes to limit global side effects (#1708, #1696)
Assuming bindings are written correctly (not by mutating the global object), two jsoo programs should be able to coexists without too much interference. I'll try to list and document the remaining side effects at some point.

[hhugo]

I'm opening ocamllabs/vscode-ocaml-platform#1617 and will close this one