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JavaScript Bridge is an easy way of calling JavaScript from Haskell, using web-sockets as the underlying transport mechanism.

High-level overview of API

JavaScript Bridge runs JavaScript fragments. The basic Haskell method is sendCommand, which sends a Text based Command to a JavaScript Engine.

sendCommand :: Engine -> Command -> IO ()

There are also ways synchronously sending a Procedure, that is a command that returns a value, and waiting the the result.

sendProcedure :: Engine -> Procedure a -> IO a

Procedure is an Applicative Functor, and a Command can be promoted into a Procedure.

Finally, there is a way of Listening for events, etc.

sendListener :: Engine -> Listener a -> (a -> IO ()) -> IO ()

Bootstrapping

First, use a middleware to setup the (Haskell) server.

import qualified Network.JavaScript as JS

        ...
        scotty 3000 $ do
          middleware $ JS.start print example

Next, include the following fragment in your HTML code, replacing localhost with your web address.

    <script>
        jsb = new WebSocket('ws://localhost:3000/');
        jsb.onmessage = function(evt){ eval(evt.data);};
    </script>

That's it!