example.hs

#!/usr/bin/env stack
-- stack script --resolver lts-12.4
{-# LANGUAGE OverloadedStrings     #-}
{-# LANGUAGE QuasiQuotes           #-}
{-# LANGUAGE TemplateHaskell       #-}
{-# LANGUAGE TypeFamilies          #-}
import           Yesod

data App = App

mkYesod "App" [parseRoutes|
/ HomeR GET
|]

instance Yesod App

getHomeR :: Handler Html
getHomeR = defaultLayout $ do
  mname <- lookupGetParam "name"

  [whamlet|
    $maybe name <- mname
      <img onload="init('#{name}')" src="https://www.yesodweb.com/static/logo-home2-no-esod-smaller2.png">
    $nothing
      No setting parameter.
  |]

  toWidget [julius|
    function init(text) {
      // anything
    }
  |]

main :: IO ()
main = warp 3000 App