I am aware that an early draft of HTML5 specified peer-to-peer connections using the PeerToPeerConnection() constructor. However, this was replaced by WebSocket which, to my knowledge, does not support peer-to-peer connections.
In addition, the device element specifies a peer-to-peer connection interface, however no web browsers have implemented it yet.
Opera Unite allows Peer to peer (basically gives your browser web server, file system and nat-traversal capabilities), but this is Opera only.
It's not exactly P2P, but you can use proxy server using push mechanism
http://en.wikipedia.org/wiki/Push_technology
For example if you want to send data from Browser A to Browser B, you send that data to proxy server and that server push it to Browser B.
来源：https://stackoverflow.com/questions/4628125/is-it-possible-to-create-peer-to-peer-connections-in-a-web-browser