How Does BrowserSync Work?
BrowserSync starts a small web server. If you’re already using a local web server or need to connect to a live website, you can start BrowserSync as a proxy server. It injects small script into every page which communicates with the server via WebSockets. When an event occurs — such as a file modification or scroll action — the server sends an update notification to all connected devices.
But you don’t need to worry about any of this; BrowserSync just works and you’ll be the envy of your peers (or accused of witchcraft).
BrowserSync 启动一个小web服务器，如果你已经在使用一个local web server或者需要连接到在线工作的website，你可以将BrowserSync作为一个proxy server来起动。它在每一个页面中主动注入一个小的脚本，该脚本通过websockets和服务器通信。当一个事件发生时，比如一个文件被修改，或者有scroll动作，这时server将发送一个update notification到所有已经连接的devices。
如果你的browsersync跑在vagrant box中，是否可以在host机器上sync浏览效果？
https://github.com/BrowserSync/browser-sync/issues/318