client.js

const { Socket } = require('net');
const readline = require('readline').createInterface({
    input: process.stdin,
    output: process.stdout,
})

const END = 'END';

const error = (message) => {
    console.error(message);
    process.exit(1);
}

const connect = (host, port) => {
    const socket = new Socket();

    console.log(`Connecting to ${host}:${port}`)
    socket.connect({ host, port });
    socket.setEncoding("utf-8");

    socket.on("connect", () => {
        console.log("Connected");

        readline.question("Choose yout username: ", (username) => {
            socket.write(username);
            console.log(`Type any message to send it, type ${END} to finish`);
        });
        readline.on("line", (message) => {
            socket.write(message);
            if (message === END) {
                socket.end();
                console.log("Disconnected");
            }
        })

        socket.on("data", (message) => {
            console.log(message);
        })
    })

    socket.on("error", (err) => error(err.message));

    socket.on("close", () => {
        process.exit(0);
    })
}

const main = () => {
    if (process.argv.length !== 4) {
        error(`Usage: node ${__filename} <host_number> <port_number>`)
    }

    let [, , host, port] = process.argv;
    if (isNaN(port)) {
        error(`Invalid port ${port}`)
    }
    port = Number(port);

    connect(host, port);
    console.log(`${host}:${port}`);
}

if (require.main === module) {
    main();
}