... and in environments which don't support the WebSocket protocol, for example, behind restrictive corporate proxies. SockJS-client does require a server counterpart, such as SockJS-node, which is a SockJS server for Node.js. The API should follow HTML5 Websockets API as closely as possible. All the transports must support cross domain connections out of the box. It's possible and recommended to host a SockJS server on a different server than your main web site.