添加网站运行时间

1.直接贴上代码（在header）：

 <script>
    function runTime() {
        var d = new Date(), str = '';
        BirthDay = new Date("March 01,2018");
        today = new Date();
        timeold = (today.getTime() - BirthDay.getTime());
        sectimeold = timeold / 1000
        secondsold = Math.floor(sectimeold);
        msPerDay = 24 * 60 * 60 * 1000
        msPerYear = 365 * 24 * 60 * 60 * 1000
        e_daysold = timeold / msPerDay
        e_yearsold = timeold / msPerYear
        daysold = Math.floor(e_daysold);
        yearsold = Math.floor(e_yearsold);
        //str = yearsold + "年";
        str += daysold + "天";
        str += d.getHours() + '时';
        str += d.getMinutes() + '分';
        str += d.getSeconds() + '秒';
        return str;
    }
    setInterval(function () { $('#run_time').html(runTime()) }, 1000);
</script>

2.在哪个地方显示就贴下下面的代码（一般在footer）：

网站已运行:<span id="run_time"></span>