What is Socket.IO's fallback mechanism?

Socket.IO implements a transport escalation strategy to maximize compatibility. By default, it first establishes an HTTP long-polling connection (which works everywhere HTTP works) and then attempts to upgrade to WebSocket once the long-polling connection is confirmed working. This ensures connectivity even in environments where WebSockets are blocked by strict firewalls, corporate proxies, or older infrastructure. If the upgrade fails, it continues over long polling with minimal disruption. You can configure Socket.IO to start with WebSocket directly (transports: ['websocket']) for better performance when you know your environment supports it. The fallback mechanism is why Socket.IO is popular in enterprise environments where network policies may block non-HTTP traffic.