问题已自行解决
var xmlhttp = new XMLHttpRequest();
xmlhttp.onreadystatechange=()=>
{
if(xmlhttp.readyState != 4)
throw new Error(“get time fail”);
var dateStr = xmlhttp.getResponseHeader("Date");
var date = new Date(dateStr);
var year = date.getFullYear();
var month = date.getMonth() + 1;
var date1 = date.getDate();
var hour = date.getHours();
var minutes = date.getMinutes();
var second = date.getSeconds();
cc.log(year + "年" + month + "月" + date1 + "日" + hour + "时" + minutes + "分" + second + "秒");
}
xmlhttp.open("GET", "https://www.baidu.com", true);
xmlhttp.setRequestHeader("If-Modified-Since", "baidu");
xmlhttp.send();