I tried to include all my rant points into this example. E.g. what if fetch() doesn't go async? Then we don't have to mark it like that and don't have to await. Where ui and commit lives? There should be a unique environment for this specific api call or a whole subsystem. objs is something both enumerable and proxied, etc. It can be done in JS, but IRL it will be:

  ./file.js:
  function foo(ctx) { // @export
    for (let x of ctx.objs.iterate()) {
      x.a = await fetch(ctx, x.b);
    }
    ctx.ui.btnok.enabled = true;
    ctx.commit();
  }
  autoexport(module, x => eval(x));

And more boilerplate, ceremony and fud down the way, if you go vanilla.

(Thank you and all commenters here for sharing your code and experience. In particular, symbol-land looks very interesting and haskell-y.)