GHCJS call callback synchronously [FAIL]

hs.hs

import GHCJS.Foreign
import GHCJS.Types

data DontTouchThis

foreign import javascript "js_testFunc" js_testFunc :: JSFun (JSRef DontTouchThis -> IO JSString) -> IO ()


main :: IO ()
main = js_testFunc =<< syncCallback1 AlwaysRetain True (\_ -> putStrLn "bar" >> return (toJSString "quux"))

js.js

js_testFunc = function(cb) {
  window.setTimeout(function() {
    debugger // Good luck
    // cb("foo") returns null, h$runSync and most other things throws an error or returns null
  }, 1000)
}