获取主机域名
function getHost(url){
var host = null;
if(typeof url=="undefined" || null == url){
url=window.location.href;
}
var regex = /^\w+\:\/\/([^\/]*).*/;
var match = url.match(regex);
if(typeof match !="undefined" && null != match){
host = match[1];
}
return host;
}