stripe.js

exports.addCardListenerImpl = function (card, fn) {
    card.addEventListener('change', fn);
    return null;
}

stripe.purs

addCardListener :: Card -> (Event -> Effect Unit) -> Effect Unit
addCardListener = runEffectFn2 addCardListenerImpl

...
eval (Init next) = next <$ do
  card <- H.liftEffect mountCard
  -- X is logged correctly and it's the stripe response object
  H.subscribe $ ES.eventSource (addCardListener card) (Just <<< H.request <<< HandleStripeError <<< spy "X")
  
eval (HandleStripeError ev reply) = do
  -- this is not logged
  logShow "HELLO?"
  pure $ reply H.Listening