求大神帮忙解决 js 如何获取服务器的问题

这段代码如何把本地时间改为使用服务器时间

<p class="endtime" id="times"></p>
<input type="hidden" id="endTime" value="2017/06/10 19:00:00">
<script type="text/javascript">
function fresh(){
    var endtime= new Date(document.getElementById("endTime").value);
    var serverTime = new Date(); 
    
    var leftsecond=parseInt((endtime.getTime()-serverTime.getTime())/1000);
    d=parseInt(leftsecond/3600/24);
    h=parseInt((leftsecond/3600)%24);
    m=parseInt((leftsecond/60)%60);
    s=parseInt(leftsecond%60);    
    var timeStr = '优惠券即将失效:&nbsp;'
                +(d>0?'<em>'+d+'</em>天':'')
                +(h>0?'<em>'+h+'</em>时':'')
                +(m>0?'<em>'+m+'</em>分':'')
                +(s>=0?'<em>'+s+'</em>秒':'');
    document.getElementById("times").innerHTML=(timeStr);
    //document.getElementById("times").innerHTML= d+"天" + h+"小时"+m+"分"+s+"秒";
    if(leftsecond<=0){
      document.getElementById("times").innerHTML="已结束";
      clearInterval(sh);
    }
}
var sh;
sh=setInterval(fresh,1000);  
</script>