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Version: 4.x

Ending notes

Final server code

index.js
const express = require('express');
const { createServer } = require('node:http');
const { join } = require('node:path');
const { Server } = require('socket.io');

const app = express();
const server = createServer(app);
const io = new Server(server);

app.get('/', (req, res) => {
res.sendFile(join(__dirname, 'index.html'));
});

io.on('connection', (socket) => {
socket.on('chat message', (msg) => {
io.emit('chat message', msg);
});
});

server.listen(3000, () => {
console.log('server running at http://localhost:3000');
});

Final client code

index.html
<!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="width=device-width,initial-scale=1.0">
<title>Socket.IO chat</title>
<style>
body { margin: 0; padding-bottom: 3rem; font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif; }

#form { background: rgba(0, 0, 0, 0.15); padding: 0.25rem; position: fixed; bottom: 0; left: 0; right: 0; display: flex; height: 3rem; box-sizing: border-box; backdrop-filter: blur(10px); }
#input { border: none; padding: 0 1rem; flex-grow: 1; border-radius: 2rem; margin: 0.25rem; }
#input:focus { outline: none; }
#form > button { background: #333; border: none; padding: 0 1rem; margin: 0.25rem; border-radius: 3px; outline: none; color: #fff; }

#messages { list-style-type: none; margin: 0; padding: 0; }
#messages > li { padding: 0.5rem 1rem; }
#messages > li:nth-child(odd) { background: #efefef; }
</style>
</head>
<body>
<ul id="messages"></ul>
<form id="form" action="">
<input id="input" autocomplete="off" /><button>Send</button>
</form>
<script src="/socket.io/socket.io.js"></script>
<script>
const socket = io();

const form = document.getElementById('form');
const input = document.getElementById('input');
const messages = document.getElementById('messages');

form.addEventListener('submit', (e) => {
e.preventDefault();
if (input.value) {
socket.emit('chat message', input.value);
input.value = '';
}
});

socket.on('chat message', (msg) => {
const item = document.createElement('li');
item.textContent = msg;
messages.appendChild(item);
window.scrollTo(0, document.body.scrollHeight);
});
</script>
</body>
</html>

Homework

Here are some ideas to improve the application:

  • Broadcast a message to connected users when someone connects or disconnects.
  • Add support for nicknames.
  • Don’t send the same message to the user that sent it. Instead, append the message directly as soon as they press enter.
  • Add “{user} is typing” functionality.
  • Show who’s online.
  • Add private messaging.
  • Share your improvements!

Getting this example

You can find it on GitHub here.

git clone https://github.com/socketio/chat-example.git
tip

You can also run this example directly in your browser on: