在撰写本文时，其他答案中只有一个正确处理DST(夏令时)转换。以下是位于加州的一个系统的结果:

                                        1/1/2013- 3/10/2013- 11/3/2013-
User       Formula                      2/1/2013  3/11/2013  11/4/2013  Result
---------  ---------------------------  --------  ---------  ---------  ---------
Miles                   (d2 - d1) / N   31        0.9583333  1.0416666  Incorrect
some         Math.floor((d2 - d1) / N)  31        0          1          Incorrect
fuentesjr    Math.round((d2 - d1) / N)  31        1          1          Correct
toloco     Math.ceiling((d2 - d1) / N)  31        1          2          Incorrect

N = 86400000

虽然数学。round返回正确的结果，我认为它有点笨拙。相反，当DST开始或结束时，通过显式计算UTC偏移量的变化，我们可以使用精确的算术:

function treatAsUTC(date) {
    var result = new Date(date);
    result.setMinutes(result.getMinutes() - result.getTimezoneOffset());
    return result;
}

function daysBetween(startDate, endDate) {
    var millisecondsPerDay = 24 * 60 * 60 * 1000;
    return (treatAsUTC(endDate) - treatAsUTC(startDate)) / millisecondsPerDay;
}

alert(daysBetween($('#first').val(), $('#second').val()));

解释

JavaScript的日期计算很棘手，因为date对象内部存储的时间是UTC，而不是本地时间。例如，3/10/2013太平洋标准时间12:00 AM (UTC-08:00)存储为3/10/2013上午8:00 UTC, 3/11/2013太平洋夏令时12:00 AM (UTC-07:00)存储为3/11/2013上午7:00 UTC。在这一天，从午夜到午夜，当地时间在UTC只有23小时!

虽然本地时间中的一天可以大于或小于24小时，但国际标准时间中的一天总是24小时上面所示的daysBetween方法利用了这一事实，它首先调用treatAsUTC将本地时间调整为午夜UTC，然后再进行减法和除法。

1. JavaScript忽略闰秒。

我来找这个小工具在里面你会找到这个的函数。这里有一个简短的例子:

        <script type="text/javascript" src="date.js"></script>
        <script type="text/javascript">
            var minutes = 1000*60;
            var hours = minutes*60;
            var days = hours*24;

            var foo_date1 = getDateFromFormat("02/10/2009", "M/d/y");
            var foo_date2 = getDateFromFormat("02/12/2009", "M/d/y");

            var diff_date = Math.round((foo_date2 - foo_date1)/days);
            alert("Diff date is: " + diff_date );
        </script>

Bookmarklet版本的其他答案，提示你两个日期:

javascript:(function() {
    var d = new Date(prompt("First Date or leave blank for today?") || Date.now());
    prompt("Days Between", Math.round(
        Math.abs(
            (d.getTime() - new Date(prompt("Date 2")).getTime())
                /(24*60*60*1000)
             )
        ));
})();

区分两个日期的最简单方法是:

var diff = Math.floor((Date.parse(str2) - Date.parse(str1)) / 86400000);

您将得到不同的天数(如果其中一个或两个都无法解析，则为NaN)。解析日期给出了以毫秒为单位的结果，要按天得到它，你必须除以24 * 60 * 60 * 1000

如果你想用天、小时、分钟、秒和毫秒来划分:

function dateDiff( str1, str2 ) {
    var diff = Date.parse( str2 ) - Date.parse( str1 ); 
    return isNaN( diff ) ? NaN : {
        diff : diff,
        ms : Math.floor( diff            % 1000 ),
        s  : Math.floor( diff /     1000 %   60 ),
        m  : Math.floor( diff /    60000 %   60 ),
        h  : Math.floor( diff /  3600000 %   24 ),
        d  : Math.floor( diff / 86400000        )
    };
}

以下是我对James版本的重构版本:

function mydiff(date1,date2,interval) {
    var second=1000, minute=second*60, hour=minute*60, day=hour*24, week=day*7;
    date1 = new Date(date1);
    date2 = new Date(date2);
    var timediff = date2 - date1;
    if (isNaN(timediff)) return NaN;
    switch (interval) {
        case "years": return date2.getFullYear() - date1.getFullYear();
        case "months": return (
            ( date2.getFullYear() * 12 + date2.getMonth() )
            -
            ( date1.getFullYear() * 12 + date1.getMonth() )
        );
        case "weeks"  : return Math.floor(timediff / week);
        case "days"   : return Math.floor(timediff / day); 
        case "hours"  : return Math.floor(timediff / hour); 
        case "minutes": return Math.floor(timediff / minute);
        case "seconds": return Math.floor(timediff / second);
        default: return undefined;
    }
}

如果我们想计算我们的年龄，这是一个有点不同的答案

    {
      birthday: 'April 22, 1993',
      names: {
        first: 'Keith',
        last: 'Buckley'
      }
    },
    {
      birthday: 'January 3, 1975',
      names: {
        first: 'Larry',
        last: 'Heep'
      }
    },
    {
      birthday: 'February 12, 1944',
      names: {
        first: 'Linda',
        last: 'Bermeer'
      }
    }
  ];
const cleanPeople = people.map(function ({birthday, names:{first, last}}) {
      // birthday, age, fullName;
      const now = new Date();
      var age =  Math.floor(( Date.parse(now) - Date.parse(birthday)) / 31536000000);
      return {
        age,
        fullName:`${first} ${last}`
      }
    });
    console.log(cleanPeople);
    console.table(cleanPeople);

试试这个

let today = new Date(). toisostring()。片(0,10) const startDate = '2021-04-15'; const endDate = today; const diffInMs = new Date(endDate) - new Date(startDate) const diffInDays = diffInMs / (1000 * 60 * 60 * 24); alert(diffInDays);