var a = new Date("2010 jan 10"),
    b = new Date("2010 jan 9");

alert(
    a + "\n" + 
    b + "\n" +
    "Difference: " + ((+a - +b) / 1000)
);

减:

var a = new Date(); 警报(“等待几秒钟，然后点击确定”); var b = new Date(); Var差= (b - a) / 1000; console.log("You waiting: " + difference + " seconds");

如果你的一个或两个日期都在未来，那么如果你想精确到秒，恐怕你就是SOL了。UTC时间有闰秒，只有在6个月之前才知道，所以任何比这更晚的日期都可能不准确几秒(在实践中，由于人们不经常更新他们的机器，您可能会发现未来的任何时间都有几秒的误差)。

这很好地解释了设计日期/时间库的理论，以及为什么会这样:http://www.boost.org/doc/libs/1_41_0/doc/html/date_time/details.html#date_time.tradeoffs

简单的方法:

function diff_hours(dt2, dt1) 
 {

  var diff =(dt2.getTime() - dt1.getTime()) / 1000;
  diff /= (60 * 60);
  return Math.abs(Math.round(diff));

 }


function diff_minutes(dt2, dt1) 
 {

  var diff =(dt2.getTime() - dt1.getTime()) / 1000;
  diff /= (60);
  return Math.abs(Math.round(diff));

 }

function diff_seconds(dt2, dt1) 
 {

  var diff =(dt2.getTime() - dt1.getTime()) / 1000;
  return Math.abs(Math.round(diff));

 }

function diff_miliseconds(dt2, dt1) 
 {

  var diff =(dt2.getTime() - dt1.getTime());
  return Math.abs(Math.round(diff));

 }


dt1 = new Date(2014,10,2);
dt2 = new Date(2014,10,3);
console.log(diff_hours(dt1, dt2));


dt1 = new Date("October 13, 2014 08:11:00");
dt2 = new Date("October 14, 2014 11:13:00");
console.log(diff_hours(dt1, dt2));

console.log(diff_minutes(dt1, dt2));

console.log(diff_seconds(dt1, dt2));

console.log(diff_miliseconds(dt1, dt2));

function parseDate(str) {
  const [dateStr, timeStr] = str.split(' ');
  const [m,d,y] = dateStr.split('/');
  const [h,min] = timeStr.split(':');
  const date = new Date(y,m,d,h,min,0, 0);
  
  return date;
}

const date1 = parseDate('28/6/2022 22:55');
const date2 = parseDate('28/6/2022 22:58');
const diffInSeconds = (date2 - date1) / 1000;

console.log(diffInSeconds)

var a = new Date("2010 jan 10"),
    b = new Date("2010 jan 9");

alert(
    a + "\n" + 
    b + "\n" +
    "Difference: " + ((+a - +b) / 1000)
);