I have a java app that functions as a server, listening to some port using the java.net.DatagramSocket class. The server is able to receive packets from some other java clients. What I did not manage to do is have a javascript client to the server. I've tried sending messages as WebSocket client

    const ws = new WebSocket("ws://localhost:9999");
    ws.addEventListener("open", () => {
        console.log("CONNECTED")
    })

But I'm getting the following error in the browser console:

App.js:9 WebSocket connection to 'ws://localhost:9999/' failed:

I've also tried using net library to send message:

    const net = require("net");
    const options = {
        post: 9999
    };
    const  client = net.createConnection(options);
    client.write("TEST")

But I'm getting the following error:

Uncaught TypeError: net.createConnection is not a function

Is there any other way to do this?