Is it possible to add your own javascript functions to a bundle?

[anfelor]

The JS FFI documentation has this example:

foreign import javascript unsafe "new Date()" current_time :: IO JSVal

but lets say I write my own date function:

foreign import javascript unsafe "myDate()" current_time :: IO JSVal

Where do I have to put myDate()'s implementation, so that it will be bundled together with the Haskell sources by ahc-dist?
More specifically, would it be possible to bundle custom functions that use sendMessage and window.onmessage in their implementation so that I can use the bundle directly as a Webworker?

[anfelor]

Yes, it is!

I use the Haskell code:

foreign import javascript unsafe "sendMessage" sendMessage' :: JSVal -> IO ()
foreign import javascript   safe "requestMessage" requestMessage' :: JSVal -> IO JSVal

sendMessage :: ToJSON a => a -> IO ()
sendMessage = sendMessage' . jsonToJSVal

requestMessage :: (ToJSON a, FromJSON b) => a -> IO (Maybe b)
requestMessage m = do
  msg <- requestMessage' $ jsonToJSVal m
  case jsonFromJSVal msg of
    Right r -> pure $ Just r
    Left _ -> pure Nothing

and modify the <project>.req.mjs file to be:

var closure = null;

onmessage = function(msg) {
    if(closure !== null) {
        var cl = closure
        closure = null;
        cl(msg.data);
    } else {
        console.log("Unhandled by Worker: ");
        console.log(msg.data);
    }
};

var requestMessage = function(msg) {
    postMessage(msg);
    return new Promise((resolve, reject) => {
        closure = resolve;
    });
};

var sendMessage = function(msg) {
    postMessage(msg);
};

export default ... __asterius_jsffi_async_mainzuMain_ajch:($1)=>__asterius_jsffi.returnFFIPromise((async () => {$1 = __asterius_jsffi.getJSValzh($1);return [1, await (requestMessage($1))];})()),__asterius_jsffi_mainzuMain_ajqL:($1)=>{$1 = __asterius_jsffi.getJSValzh($1);return (sendMessage($1));}}}) ...

This means that I can't use the --bundle option and have to bundle manually (in the asterius shell) by calling npx webpack --mode production --entry ./<project>.mjs --output-path . --output-filename <project>.js after replacing the above file. Then you need to place the <project>.wasm file into the root folder of your server and you can call the <project>.js file as a Webworker.