What is useEffect in React?

Direct answer

useEffect is a Hook for synchronizing a component with an external system after React commits an update.

Typical external systems include network connections, browser APIs, subscriptions, timers, analytics integrations, or third-party widgets.

chat-effect.js

useEffect(() => {
  const connection = createConnection(roomId);
  connection.connect();

  return () => connection.disconnect();
}, [roomId]);