Brr: WorkerGlobalScope?

zeroexcuses · May 7, 2023, 2:19am

I have a piece of OCaml/Brr/js_of_ocaml code running inside a WebWorker.

How do I grab the WorkerGlobalScope - Web APIs | MDN via self (or any other way) ?

Thanks!

hhugo · May 8, 2023, 2:15pm

In jsoo, I would expect Js.Unsafe.global to work.

dbuenzli · May 8, 2023, 2:41pm

In brr it doesn’t take a long time to discover Jv.global via the API docs or the FFI manual.

zeroexcuses · May 8, 2023, 3:03pm

Maybe this is due to my lack of JS knowledge, it was not obvious to me that JS “globalThis” is actually a WorkerGlobalScope: globalThis - JavaScript | MDN

The first thing I tried, was rg "WorkerGlobalScope" which only returns one line:

github.com

dbuenzli/brr/blob/master/src/brr_webworkers.ml#L46


      
            type t = Jv.t
            include (Jv.Id : Jv.CONV with type t := t)
            let shared = Jv.get Jv.global "SharedWorker"
            let create ?(opts = Jv.undefined) uri =
              Jv.new' shared Jv.[| of_jstr uri; opts |]
          
          
  external as_target : t -> Ev.target = "%identity"
            let port w = Message.Port.of_jv @@ Jv.get w "port"
          end
          
          
let ami () = Jv.has "WorkerGlobalScope" Jv.global
          module G = struct
            let import_scripts uris =
              ignore @@ Jv.call Jv.global "importScripts" [|Jv.of_jstr_list uris|]
          
          
  let post ?opts v =
              let opts = match opts with None -> Jv.undefined | Some o -> Obj.magic o in
              ignore @@ Jv.call Jv.global "postMessage" [| Jv.repr v; opts |]
          
          
  let close () = ignore @@ Jv.call Jv.global "close" [||]
          end

let ami () = Jv.has “WorkerGlobalScope” Jv.global

Now, with 2020 hindsight, one could argue: you should then see that Jv.global is what you’re after.

However, I’d argue on the contrary that line seems to suggest that Jv.global is NOT what I want, and instead, I want to somehow fetch the “WorkerGlobalScope” field of Jv.global .

The next thing that came to mind was: perhaps there is a module named WorkerGlobalScope, and if we find it ,we find some object of type WorkerGlobalScope.t and we’re done.

This leads to rg WorkerGlobalScope (without the “”). In addition to the previous *.ml file, this now brings up a number of *.mli files, where WorkerGlboalScope is mentioned in a comment pointing at MDN.

For whatever reason, WorkerGlobalScope - Web APIs | MDN currently does not mention the word “globalThis”

Conditioned on knowing that WorkerGlobalScope == globalThis, this is easy to resolve; however, until knowing that WorkerGlobalScope == globalThis, it is not obvious to me how one makes the jump from WorkerGlobalScope to Jv.global