javascript - 为什么这个倒计时时钟代码会返回一个未定义的字符串？

Question

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Answer 1

理想情况下，我会倾向于使用 .textContent javascript 属性，而不是 document.write:

var displayTimer = document.getElementsByClassName('display-timer')[0];

function startTimer(duration) {

  setInterval(function() {
    var timer = duration - (new Date).getTime() / 1000;
    var minutes = parseInt(timer / 60, 10)
    var seconds = parseInt(timer % 60, 10);
    minutes = minutes < 10 ? "0" + minutes : minutes;
    seconds = seconds < 10 ? "0" + seconds : seconds;
    var display = "Ends in " + minutes + " mins and " + seconds + " secs";

    if (--timer < 0) {
      display = "Ended";
    }

    displayTimer.textContent = display;

  }, 1000);
}

window.addEventListener('load',function(){startTimer(999999999999999);},false);

<div class="display-timer">
</div>