$(document).ready(function() {
      let ifClass = document.getElementsByClassName('timer_text');
      if (ifClass.length > 0) {
        var spd = 100;
        var spdVal = 10;
        var cntDown = 10 * 60 * spdVal;
        setInterval(function() {
          var mn, sc, ms;
          cntDown--;
          if (cntDown < 0) {
            return false;
          }
          mn = Math.floor((cntDown / spdVal) / 60);
          mn = (mn < 10 ? '0' + mn : mn);
          sc = Math.floor((cntDown / spdVal) % 60);
          sc = (sc < 10 ? '0' + sc : sc);
          ms = Math.floor(cntDown % spdVal);
          ms = (ms < 10 ? '0' + ms : ms);
          var result = mn + ':' + sc;
          document.getElementById('co_timer').innerHTML = result;
        }, spd);
      }
    });