javascript - 如何在javascript中获取两个日期之间的秒数？

Question

我正在尝试获取 javascript 中两个日期之间的秒数。
问题 here和here建议一个简单的减法操作就可以解决问题，其他答案建议您使用 .getTime() 或 .valueOf() 属性。
但尽管如此，当我减去相隔 5 秒的两个日期时，我得到的值 1551181475795 太大了，无法正确。
这是我的代码:

var countDownDate = new Date("Mar 16, 2019 16:33:25").valueOf();
var dist = 347155200;
// Update the count down every 1 second
var x = setInterval(function() {

  // Get todays date and time
  var now = new Date("Mar 16, 2019 16:33:30");

  // Find the distance between now and the count down date
  var distance = Math.abs(now - countDownDate / 1000);
  // Display the result in the element with id="demo"
  document.getElementById("demo").innerHTML = distance;

  // If the count down is finished, write some text
  if (distance < 0) {
    clearInterval(x);
    document.getElementById("demo").innerHTML = "EXPIRED";
  }
}, 1000);

<p id='demo'>

正如您所见，两个时间仅相差 5 秒，但分隔它们的值没有任何意义。
提前致谢!

Answer 1

这是一个运算顺序问题，在进行减法之前，您需要将 countDownDate 除以 1000(您正在计算 now - countDownDate/1000 但是，您应该计算 (now - countDownDate)/1000，先减法):

var countDownDate = new Date("Mar 16, 2019 16:33:25").valueOf();
var dist = 347155200;
// Update the count down every 1 second
var x = setInterval(function() {

  // Get todays date and time
  var now = new Date("Mar 16, 2019 16:33:30");

  // Find the distance between now and the count down date
  var distance = Math.abs((now - countDownDate) / 1000);
  // Display the result in the element with id="demo"
  document.getElementById("demo").innerHTML = distance;

  // If the count down is finished, write some text
  if (distance < 0) {
    clearInterval(x);
    document.getElementById("demo").innerHTML = "EXPIRED";
  }
}, 1000);

<p id="demo"></p>