到达结束时间后倒数

Question

我目前正在研究CountDown。但是，我试图在到达日期后显示其他显示。任何建议都将受到高度赞赏。一旦间隔小于0，就无法ping if语句中不起作用的内容。

     const second = 1000,
          minute = second * 60,
          hour = minute * 60,
          day = hour * 24;

    let countDown = new Date('Sep 06, 2018 23:00:00').getTime(),
        x = setInterval(function() {

          let now = new Date().getTime(),
              distance = countDown - now;

          document.getElementById('days').innerText = Math.floor(distance / (day)),
            document.getElementById('hours').innerText = Math.floor((distance % (day)) / (hour)),
            document.getElementById('minutes').innerText = Math.floor((distance % (hour)) / (minute)),
            document.getElementById('seconds').innerText = Math.floor((distance % (minute)) / second);

          //do something later when date is reached
        if (distance < 0) {
         clearInterval(x);
          'its  time!';
         } 
//if (distance < 0) {
  //       clearInterval(x);
// document.getElementById('head').innerText=  'its Time';
      //}

        }, second) 

html: 

    <div class="container">
  <h1 id="head">My birthday Coming Soon:</h1>
  <ul>
    <li><span id="days"></span>days</li>
    <li><span id="hours"></span>Hours</li>
    <li><span id="minutes"></span>Minutes</li>
    <li><span id="seconds"></span>Seconds</li>
  </ul>
</div>