Adding Reading Time to Hexo + Butterfly

 1let oSpan = document.getElementsByTagName("readtime");
 2let localhostTime = new Date(); // Get the time when the page is opened
 3function tow(n) {
 4  return n >= 0 && n < 10 ? "0" + n : "" + n;
 5}
 6setInterval(function () {
 7  let goTime = new Date(); // Get the dynamic time
 8  let diffTime = goTime.getTime() - localhostTime.getTime();
 9  var second = Math.floor(diffTime / 1000); // Seconds from the future time to now
10  second = second % 86400; // The remainder represents the remaining seconds;
11  var hour = Math.floor(second / 3600); // The integer part represents hours;
12  second %= 3600; // The remainder represents the remaining seconds;
13  var minute = Math.floor(second / 60);
14  second %= 60;
15  // var str = tow(day) + '<span class="time">days</span>'
16  var str =
17    tow(hour) +
18    '<span class="time">hours</span>' +
19    tow(minute) +
20    '<span class="time">minutes</span>' +
21    tow(second) +
22    '<span class="time">seconds</span>';
23  oSpan.innerHTML = "You have been browsing this page for " + str;
24}, 1000);

1- <script src="/js/readtime.js"></script>