"Under the hood SockJS tries to use native WebSockets first. If that fails it can use a variety of browser-specific transport protocols and presents them through WebSocket-like abstractions." - SockJS

How this is helping?

"Flash is absolutely not required for Socket.IO to function. If Flash is available, it'll be leveraged, as it provides almost the same capabilities as WebSocket. If it's not, the next best transport will be chosen." - Socket.io