设置网站运行时间

/**
 * 底部运行时间计算（记得设置html<span id="old-now"></span>）
 */
function showDatetime() {
  window.setTimeout("showDatetime()", 1000);
  let BirthDay = new Date("08/01/2019 00:00:00");
  let today = new Date();
  let timeold = (today.getTime() - BirthDay.getTime());
  let sectimeold = timeold / 1000;
  secondsold = Math.floor(sectimeold);
  let msPerDay = 24 * 60 * 60 * 1000;
  let e_daysold = timeold / msPerDay;
  let daysold = Math.floor(e_daysold);
  let e_hrsold = (e_daysold - daysold) * 24;
  let hrsold = setZero(Math.floor(e_hrsold));
  let e_minsold = (e_hrsold - hrsold) * 60;
  let minsold = setZero(Math.floor((e_hrsold - hrsold) * 60));
  let seconds = setZero(Math.floor((e_minsold - minsold) * 60));
  document.querySelector('#old-now').innerHTML = "&nbsp已运行&nbsp;" + daysold + "&nbsp天&nbsp" + hrsold + "&nbsp小时&nbsp" + minsold + "&nbsp分&nbsp<strong style='color:#A52A2A'>" + seconds + "</strong>&nbsp秒";
}

/**
 * 归零
 * @param {Integer} nothing。
 */
function setZero(i) {
  if (i < 10) {
    i = "0" + i;
  }
  return i;
}

function createTime() {
  var now = new Date();
  var run = new Date("05/28/2018 20:01:01");
  //总秒数
  var runTime = (now - run) / 1000,
    days = Math.floor(runTime / 60 / 60 / 24),
    hours = Math.floor(runTime / 60 / 60 - (24 * days)),
    minutes = Math.floor(runTime / 60 - (24 * 60 * days) - (60 * hours)),
    seconds = Math.floor((now - run) / 1000 - (24 * 60 * 60 * days) - (60 * 60 * hours) - (60 * minutes));
  //前置零
  if (String(hours).length === 1) {
    hours = "0" + hours;
  }
  if (String(minutes).length === 1) {
    minutes = "0" + minutes;
  }
  if (String(seconds).length === 1) {
    seconds = "0" + seconds;
  }
  /*document.querySelector(".run-times").innerHTML = days + " 天 " + hours
          + " 时 " + minutes + " 分 " + seconds + " 秒";
  */
  document.querySelector(".run-times").innerHTML = "RunTime: " + days + "," + hours
          + ":" + minutes + ":" + seconds + "";
  
}

//setInterval("createTime()", 500);
if (!document.hidden) {
  var siteTime = setInterval("createTime()", 500);
} else {
  clearInterval(siteTime);
}




/**
 * HTML写法
<span class="run-times" title="网站运行时间">载入中...</span>
<p class="run-times" title="主页运行时间">RunTime Loading...</p>
*/