Working chat example from https://javascript.info/websocket#chat-example

client.js

/* global WebSocket */
const socket = new WebSocket('ws://localhost:8080')

// send message from the form
document.forms.publish.onsubmit = function () {
  const outgoingMessage = this.message.value

  socket.send(outgoingMessage)
  return false
}

// message received - show the message in div#messages
socket.onmessage = async function (event) {
  const message = await event.data.text()

  const messageElem = document.createElement('div')
  messageElem.textContent = message
  console.log(message)
  document.getElementById('messages').prepend(messageElem)
}

index.html

<!-- message form -->
<form name="publish">
  <input type="text" name="message">
  <input type="submit" value="Send">
</form>

<!-- div with messages -->
<div id="messages"></div>

<script src="client.js"></script>

package.json

{
  "scripts": {
    "start": "npm-run-all --parallel frontend backend",
    "backend": "nodemon --ignore client.js server.js",
    "frontend": "browser-sync start --server --files \"*.html,client.js\"",
    "test": "standard --fix"
  },
  "type": "module",
  "dependencies": {
    "ws": "^8.18.3"
  },
  "devDependencies": {
    "browser-sync": "^3.0.4",
    "nodemon": "^3.1.10",
    "npm-run-all": "^4.1.5",
    "standard": "^17.1.2"
  }
}

server.js

import { WebSocketServer } from 'ws'

const wss = new WebSocketServer({ port: 8080 })

const clients = new Set()

wss.on('connection', onSocketConnect)

function onSocketConnect (ws) {
  clients.add(ws)

  ws.on('message', function (message) {
    message = message.slice(0, 50) // max message length will be 50

    for (const client of clients) {
      client.send(message)
    }
  })

  ws.on('close', function () {
    clients.delete(ws)
  })
}