Example of do some stuff before link redirect

Main.hs

{-# LANGUAGE CPP #-}
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE ScopedTypeVariables #-}

module Main where

import Control.Monad ( void )
import Control.Monad.IO.Class ( liftIO )
import Data.Map as Map
import Data.Text as T
import Language.Javascript.JSaddle
-- import Lens.Micro.Platform
import Reflex.Dom

main :: IO ()
main = mainWidgetWithHead header body

header :: MonadWidget t m => m ()
header = do
  (ev, fire) <- newTriggerEvent
  liftIO $ fire ()
  meta
  dyEvMT <- widgetHold (return never) $ cssFile "https://cdnjs.cloudflare.com/ajax/libs/materialize/1.0.0/css/materialize.min.css" <$ ev
  _ <- widgetHold (return never) $ cssFile "https://fonts.googleapis.com/icon?family=Material+Icons" <$ switchPromptlyDyn dyEvMT
  return ()

body :: MonadWidget t m => m ()
body = do
  ev <- lynk "I'm a link"
  ev' <- doStuff (traceEvent "I did stuff" ev)
  performEvent_ (liftJSM goAway <$ ev')

lynk :: MonadWidget t m => Text -> m (Event t ())
lynk t = do
  (l, _) <- elAttr' "a" (Map.fromList [("href","javascript:void(0);")]) $ text t
  return $ domEvent Click l

doStuff :: MonadWidget t m => Event t () -> m (Event t ())
doStuff ev = do
  evDec::(Event t (Maybe Text)) <- getAndDecode ("https://www.reddit.com/r/javascript.json" <$ ev)
  return $ () <$ evDec

goAway :: JSM ()
goAway = void $ eval ("window.location.assign('https://www.w3schools.com')"::Text)

meta :: MonadWidget t m => m ()
meta = elAttr "meta" (Map.fromList [
      ("name", "viewport")
    , ("content", "width=device-width,initial-scale=1")
    , ("charset", "UTF-8")
  ]) $ return ()

cssFile :: MonadWidget t m => Text -> m (Event t ())
cssFile r = do
  (e, _) <- elAttr' "link" (Map.fromList [
      ("rel", "stylesheet")
    , ("type", "text/css")
    , ("href", r)]) $ return ()
  return $ domEvent Load e