minimal chat

index.js

const net = require('net');

const isServer = process.argv[2] == 'server';
const port = process.argv[3]; // server port

const display = (data) => console.log('> ' + data.toString().trim());

let send = null;

if (isServer) {
    const friends = new Set;
    const server = net.createServer((socket) => {
        console.log('new peer connecting');
        socket.on('error', (err) => console.error('Peer error', err));
        socket.on('data', (data) => (display(data), send(data)));
        socket.on('end', () => (friends.delete(socket), console.log('Peer disconnected')));
        friends.add(socket);
    });
    server.listen(port);
    send = (data) => friends.forEach(f => f.write(data));
} else {
    const socket = net.connect(port);
    socket.on('error', (err) => console.error('Socket error', err));
    socket.on('data', display);
    socket.on('end', () => (console.log('Server disconnected'), process.exit(0)));
    send = (data) => socket.write(data);
}

process.stdin.resume();
process.stdin.on('data', send);

Usage:
node . server 4567
node . client 4567