客户端是靠不住的:)我们要取服务器的时间

function get_server_time(url){
var xmlhttp = new XMLHttpRequest();
xmlhttp.open("GET",url, false);
xmlhttp.setRequestHeader("If-Modified-Since","0");
xmlhttp.send(null);
return new Date(xmlhttp.getResponseHeader("Date"));
}
var now = get_server_time("http://www.douban.com/service/auth/request_token")
alert(now );
alert(now.getTime() );