A Real-Time Chat in 50 Lines

WebSockets sound complex until you realize a chat server is just broadcasting messages. Here’s the minimal version.

Server

const express = require("express");
const http = require("http");
const WebSocket = require("ws");

const app = express();
const server = http.createServer(app);
const wss = new WebSocket.Server({ server });

app.use(express.static("public"));

wss.on("connection", ws => {
  ws.on("message", message => {
    wss.clients.forEach(client => {
      if (client.readyState === WebSocket.OPEN) {
        client.send(message);
      }
    });
  });
});

server.listen(3000);

That’s it. Any message from any client goes to every connected client.

Client

<ul id="messages"></ul>
<form id="form"><input id="input" /><button>Send</button></form>
<script>
  const ws = new WebSocket("ws://localhost:3000");
  ws.onmessage = e => {
    const li = document.createElement("li");
    li.textContent = e.data;
    document.getElementById("messages").appendChild(li);
  };
  document.getElementById("form").onsubmit = e => {
    e.preventDefault();
    ws.send(document.getElementById("input").value);
    document.getElementById("input").value = "";
  };
</script>

What This Doesn’t Do

• Authentication: anyone can connect.
• Persistence: messages disappear when the server restarts.
• Scalability: this broadcasts in-memory. For multiple servers, you need Redis or a message broker.

But it’s enough to understand how WebSockets work. Everything else is layering on top of this.