js 實現的倒計時的函數

   function countTime() {
    //獲取當前時間  
    var date = new Date();
    var now = date.getTime();
    var d = 0;
    var h = 0;
    var m = 0;
    var s = 0;
    //設置截止時間  
    var str = "{$activity_info.signup_end_time}";
    var endDate = new Date(str);
    var end = endDate.getTime();

    //時間差  
    var leftTime = end - now;
    //定義變量 d,h,m,s保存倒計時的時間  
    var d, h, m, s;
    if (leftTime >= 0) {
        d = Math.floor(leftTime / 1000 / 60 / 60 / 24);
        h = Math.floor(leftTime / 1000 / 60 / 60 % 24);
        m = Math.floor(leftTime / 1000 / 60 % 60);
        s = Math.floor(leftTime / 1000 % 60);
    }
    //將倒計時賦值到div中  
    var strhtml = "報名倒計時：";
    if (d > 0) {
        strhtml += "還有 " + d + " 天";
    }

    if (h > 0) {
        strhtml += " " + h + " 時";
    }

    if (m > 0) {
        strhtml += " " + m + " 分";
    }

    if (s > 0) {
        strhtml += " " + s + " 秒";
    }

    if(d=='0' && h=='0' && m=='0' && s=='0') {
        strhtml += " 活動已結束";
    document.getElementById("signup_body1").style.display='block';
    document.getElementById("signup_body2").style.display='none';
    }

    // console.log(d,h,m,s);
    document.getElementById("sigup_countdown").innerHTML = strhtml;
    //遞歸每秒調用countTime方法，顯示動態時間效果  
    setTimeout(countTime, 1000);

}

  <div class="am-g">
    <div class="am-u-sm-12" id="sigup_countdown"></div>
  </div>