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 SockJS模拟 WebSocket ：为websocket的实现提供了多套后备方案，当浏览器不支持websocket时，她可以选择不同的方案实现，并且完全与websocket的特性一样的。

下面是官方的一些简介：

SockJS-client

SockJS is a browser JavaScript library that provides a WebSocket-like object. SockJS gives you a coherent, cross-browser, Javascript API which creates a low latency, full duplex, cross-domain communication channel between the browser and the web server.

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 is intended to work for all modern browsers and in environments which don\'t support the WebSocket protocol -- for example, behind restrictive corporate proxies.

SockJS-client does require a server counterpart:

• SockJS-node is a SockJS server for Node.js.

Philosophy:

• 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.
• There is support for at least one streaming protocol for every major browser.
• Streaming transports should work cross-domain and should support cookies (for cookie-based sticky sessions).
• Polling transports are used as a fallback for old browsers and hosts behind restrictive proxies.
• Connection establishment should be fast and lightweight.
• No Flash inside (no need to open port 843 - which doesn\'t work through proxies, no need to host \'crossdomain.xml\', no need to wait for 3 seconds in order to detect problems)

Subscribe to SockJS mailing list for discussions and support.

SockJS family:

• SockJS-client JavaScript client library
• SockJS-node Node.js server
• SockJS-erlang Erlang server
• SockJS-cyclone Python/Cyclone/Twisted server
• SockJS-tornado Python/Tornado server
• SockJS-twisted Python/Twisted server
• Spring Framework Java client & server
• vert.x Java/vert.x server
• Xitrum Scala server
• Atmosphere Framework JavaEE Server, Play Framework, Netty, Vert.x

Work in progress:

• SockJS-ruby
• SockJS-netty
• SockJS-gevent (SockJS-gevent fork)
• pyramid-SockJS
• wildcloud-websockets
• wai-SockJS
• SockJS-perl
• SockJS-go

Getting Started

SockJS mimics the WebSockets API, but instead of WebSocket there is a SockJS Javascript object.

First, you need to load the SockJS JavaScript library. For example, you can put that in your HTML head: