计算两个日期之间天数的简单方法是去掉它们的时间分量，即将小时、分钟、秒和毫秒设置为0，然后减去它们的时间，用一天的毫秒值来计算。

var firstDate= new Date(firstDate.setHours(0,0,0,0));
var secondDate= new Date(secondDate.setHours(0,0,0,0));
var timeDiff = firstDate.getTime() - secondDate.getTime();
var diffDays =timeDiff / (1000 * 3600 * 24);

使用以下公式可以计算出两个不同TZs的休止日期之间的完整证明天数差:

var start = new Date('10/3/2015'); var end = new Date('11/2/2015'); Var天数= (end - start) / 1000 / 60 / 60 / 24; console.log(天); //实际上是30;但由于夏令时，将显示31.0xxx //你需要抵消如下 days = days - (end.getTimezoneOffset() - start.getTimezoneOffset()) / (60 * 24); console.log(天);

 // JavaScript / NodeJs answer  
   let startDate = new Date("2022-09-19");
   let endDate = new Date("2022-09-26");

   let difference = startDate.getTime() - endDate.getTime();
   
    console.log(difference);

   let TotalDiffDays = Math.ceil(difference / (1000 * 3600 * 24));
   console.log(TotalDiffDays + " days :) ");

下面是datediff的快速实现，作为解决问题的概念证明。它依赖于这样一个事实，即您可以通过减去两个日期之间经过的毫秒，这将它们强制转换为原始数字值(自1970年初以来的毫秒)。

/** * Take the difference between the dates and divide by milliseconds per day. * Round to nearest whole number to deal with DST. */ function datediff(first, second) { return Math.round((second - first) / (1000 * 60 * 60 * 24)); } /** * new Date("dateString") is browser-dependent and discouraged, so we'll write * a simple parse function for U.S. date format (which does no error checking) */ function parseDate(str) { var mdy = str.split('/'); return new Date(mdy[2], mdy[0] - 1, mdy[1]); } alert(datediff(parseDate(first.value), parseDate(second.value))); <input id="first" value="1/1/2000"/> <input id="second" value="1/1/2001"/>

You should be aware that the "normal" Date APIs (without "UTC" in the name) operate in the local timezone of the user's browser, so in general you could run into issues if your user is in a timezone that you don't expect, and your code will have to deal with Daylight Saving Time transitions. You should carefully read the documentation for the Date object and its methods, and for anything more complicated, strongly consider using a library that offers more safe and powerful APIs for date manipulation.

数字和日期——MDN JavaScript指南 日期——MDN JavaScript参考

同样，出于说明的目的，为了简洁起见，该代码段对窗口对象使用了命名访问，但在生产中应该使用getElementById之类的标准化api，或者更有可能使用一些UI框架。

我使用下面的代码来试验新闻帖子的发布日期功能。我根据发布日期和当前日期计算分钟、小时、天或年。

var startDate= new Date("Mon Jan 01 2007 11:00:00");
var endDate  =new Date("Tue Jan 02 2007 12:50:00");
var timeStart = startDate.getTime();
var timeEnd = endDate.getTime();
var yearStart = startDate.getFullYear();
var yearEnd   = endDate.getFullYear();
if(yearStart == yearEnd)
 {
  var hourDiff = timeEnd - timeStart; 
  var secDiff = hourDiff / 1000;
  var minDiff = hourDiff / 60 / 1000; 
  var hDiff = hourDiff / 3600 / 1000; 
  var myObj = {};
  myObj.hours = Math.floor(hDiff);
  myObj.minutes = minDiff  
  if(myObj.hours >= 24)
   {
    console.log(Math.floor(myObj.hours/24) + "day(s) ago")
   } 
 else if(myObj.hours>0)
  {
   console.log(myObj.hours +"hour(s) ago")
  }
 else
  {
   console.log(Math.abs(myObj.minutes) +"minute(s) ago")
  }
}
else
{
var yearDiff = yearEnd - yearStart;
console.log( yearDiff +" year(s) ago");
}

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);