const ws = new WebSocket("wss://…") upgrades to a live socket. Handle onopen, onmessage, onclose, onerror; send with ws.send(data). Unlike fetch (request/response), the server can push at any time. Use wss:// on HTTPS pages, and add your own reconnect logic — it needs a WebSocket server, so it can't run in this offline sandbox.
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<body style="background:#06040d;color:#e6e0ff;font-family:monospace;padding:20px"><pre>const ws = new WebSocket('wss://echo.websocket.events');
ws.onopen = () => ws.send('hello');
ws.onmessage = e => console.log('←', e.data);
ws.onclose = () => {/* reconnect here */};</pre></body></html>