Attributes of Errors are not preserved across realms

Consider the following example:

// worker.js
importScripts("./iife/synclink.js");

function raiseFromWorker(){
    const err = new Error("hi!");
    err.xxx = 42;
    throw err;
}

Synclink.expose(raiseFromWorker);

<!-- index.html >
<html>
  <head>
    <script>
      async function main() {
          const Synclink = await import("./esm/synclink.mjs");
          let raiseFromWorker = Synclink.wrap(new Worker("worker.js"))
          try {
              await raiseFromWorker();
          }
          catch(err) {
              //console.log(err);
              console.log(err.message);
              console.log(err.xxx);
          }
      }
      main();
    </script>
  </head>
</html>

The attribute xxx is not preserved across the boundary. I think it would be nice/useful/expected that it is. For example, this would remove the need for this ugly hack in pyscript: https://github.com/pyscript/pyscript/blob/b247864414ae813b6ff73792d10a344bc4d477f9/pyscriptjs/src/main.ts#L30-L41

If I understand correctly, the relevant code is here: https://github.com/hoodmane/synclink/blob/cc08aab7d28f5b5573c80a3766714944bf666160/src/transfer_handlers.ts#L156-L164

would it be possible to iterate over all attributes and transfer them?

pyodide / synclink

Attributes of Errors are not preserved across realms #18