WebSocket

A WebSocket is a long-lived connection over which client and server can both send messages at any time, instead of the app asking with a new HTTP request each time. React Native provides the same global WebSocket class as browsers, implemented natively on iOS and Android, so standard WebSocket client code works unchanged.

const ws = new WebSocket('wss://realtime.example.com/feed');

ws.onopen = () => ws.send(JSON.stringify({ subscribe: 'prices' }));
ws.onmessage = (event) => handle(JSON.parse(event.data));
ws.onclose = (event) => scheduleReconnect(event.code);

It powers chat, live scores, collaborative editing, delivery tracking and most hosted “realtime” features, including those of Supabase and Firebase, which manage the connection for you.

The mobile reality is that connections drop constantly, and code written for a desktop browser does not expect it:

• Backgrounding kills it. When the app goes to the background, iOS suspends it within seconds and the socket dies. Listen to AppState and reconnect when the app becomes active again.
• Network changes kill it. Moving from Wi-Fi to cellular or through a tunnel drops the connection, sometimes without a clean onclose for a while. Use heartbeats (ping messages with a timeout) to detect dead connections.
• Reconnect with backoff. Retrying instantly in a loop drains battery and can hammer your server when it comes back up. Increase the delay between attempts.
• Resync after reconnecting. Messages sent while the app was disconnected are gone. Fetch what you missed over HTTP when the socket reopens.

Two misconceptions: Socket.IO is its own protocol on top of WebSockets, so a plain WebSocket cannot talk to a Socket.IO server; and a WebSocket cannot keep running in the background to deliver messages. For reaching a user when the app is closed, use push notifications.