它称为“
同源起源策略”。简而言之：您的代码所在的域是您的Javascript可以与之通信的唯一域（默认情况下）
您会收到如下错误：
XMLHttpRequest cannot load http://maps.googleapis.com/maps/api/geopre/json?address=1600+Amphitheatre+Parkway,+Mountain+View,+CA&sensor=false. Origin http://fiddle.jshell.net is not allowed by Access-Control-Allow-Origin.
