This library lets you derive automatically Javascript functions that let you query each endpoint of a servant webservice.
It contains a powerful system allowing you to generate functions for several frameworks (Angular, AXios, JQuery) as well as vanilla (framework-free) javascript code.
Read more about the following example here.
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE TypeOperators #-}
{-# LANGUAGE DeriveGeneric #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
import Control.Concurrent.STM
import Control.Monad.IO.Class
import Data.Aeson
import Data.Proxy
import GHC.Generics
import Network.Wai.Handler.Warp (run)
import Servant
import Servant.JS
import System.FilePath
-- * A simple Counter data type
newtype Counter = Counter { value :: Int }
deriving (Generic, Show, Num)
instance ToJSON Counter
-- * Shared counter operations
-- Creating a counter that starts from 0
newCounter :: IO (TVar Counter)
newCounter = newTVarIO 0
-- Increasing the counter by 1
counterPlusOne :: MonadIO m => TVar Counter -> m Counter
counterPlusOne counter = liftIO . atomically $ do
oldValue <- readTVar counter
let newValue = oldValue + 1
writeTVar counter newValue
return newValue
currentValue :: MonadIO m => TVar Counter -> m Counter
currentValue counter = liftIO $ readTVarIO counter
-- * Our API type
type TestApi = "counter" :> Post '[JSON] Counter -- endpoint for increasing the counter
:<|> "counter" :> Get '[JSON] Counter -- endpoint to get the current value
type TestApi' = TestApi -- The API we want a JS handler for
:<|> Raw -- used for serving static files
-- this proxy only targets the proper endpoints of our API,
-- not the static file serving bit
testApi :: Proxy TestApi
testApi = Proxy
-- this proxy targets everything
testApi' :: Proxy TestApi'
testApi' = Proxy
-- * Server-side handler
-- where our static files reside
www :: FilePath
www = "examples/www"
-- defining handlers
server :: TVar Counter -> Server TestApi
server counter = counterPlusOne counter -- (+1) on the TVar
:<|> currentValue counter -- read the TVar
server' :: TVar Counter -> Server TestApi'
server' counter = server counter
:<|> serveDirectory www -- serve static files
runServer :: TVar Counter -- ^ shared variable for the counter
-> Int -- ^ port the server should listen on
-> IO ()
runServer var port = run port (serve testApi' $ server' var)
main :: IO ()
main = do
-- write the JS code to www/api.js at startup
writeJSForAPI testApi jquery (www </> "api.js")
-- setup a shared counter
cnt <- newCounter
-- listen to requests on port 8080
runServer cnt 8080
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