function getSeverDateTime (){
var xhr = window.ActiveXObject ? new ActiveXObject("Microsoft.XMLHTTP") : new XMLHttpRequest();
xhr.open("HEAD", window.location.href, false);
xhr.send();
var d= new Date(xhr.getResponseHeader("Date"));
return d;
}
原文：http://www.cnblogs.com/smjia/p/4466678.html