不久前，我做了一个这样的函数:

function getAge(birthDate) {
  var now = new Date();

  function isLeap(year) {
    return year % 4 == 0 && (year % 100 != 0 || year % 400 == 0);
  }

  // days since the birthdate    
  var days = Math.floor((now.getTime() - birthDate.getTime())/1000/60/60/24);
  var age = 0;
  // iterate the years
  for (var y = birthDate.getFullYear(); y <= now.getFullYear(); y++){
    var daysInYear = isLeap(y) ? 366 : 365;
    if (days >= daysInYear){
      days -= daysInYear;
      age++;
      // increment the age only if there are available enough days for the year.
    }
  }
  return age;
}

它接受一个Date对象作为输入，所以你需要解析'YYYYMMDD'格式的日期字符串:

var birthDateStr = '19840831',
    parts = birthDateStr.match(/(\d{4})(\d{2})(\d{2})/),
    dateObj = new Date(parts[1], parts[2]-1, parts[3]); // months 0-based!

getAge(dateObj); // 26

我认为可以简单地像这样:

function age(dateString){
    let birth = new Date(dateString);
    let now = new Date();
    let beforeBirth = ((() => {birth.setDate(now.getDate());birth.setMonth(now.getMonth()); return birth.getTime()})() < birth.getTime()) ? 0 : 1;
    return now.getFullYear() - birth.getFullYear() - beforeBirth;
}

age('09/20/1981');
//35

也适用于时间戳

age(403501000000)
//34

为了测试生日是否已经过去，我定义了一个帮助函数Date.prototype。getDoY，它有效地返回一年中的天数。剩下的就不言自明了。

Date.prototype.getDoY = function() {
    var onejan = new Date(this.getFullYear(), 0, 1);
    return Math.floor(((this - onejan) / 86400000) + 1);
};

function getAge(birthDate) {
    function isLeap(year) {
        return year % 4 == 0 && (year % 100 != 0 || year % 400 == 0);
    }

    var now = new Date(),
        age = now.getFullYear() - birthDate.getFullYear(),
        doyNow = now.getDoY(),
        doyBirth = birthDate.getDoY();

    // normalize day-of-year in leap years
    if (isLeap(now.getFullYear()) && doyNow > 58 && doyBirth > 59)
        doyNow--;

    if (isLeap(birthDate.getFullYear()) && doyNow > 58 && doyBirth > 59)
        doyBirth--;

    if (doyNow <= doyBirth)
        age--;  // birthday not yet passed this year, so -1

    return age;
};

var myBirth = new Date(2001, 6, 4);
console.log(getAge(myBirth));

从日期选择器计算年龄

         $('#ContentPlaceHolder1_dob').on('changeDate', function (ev) {
            $(this).datepicker('hide');

            //alert($(this).val());
            var date = formatDate($(this).val()); // ('2010/01/18') to ("1990/4/16"))
            var age = getAge(date);

            $("#ContentPlaceHolder1_age").val(age);
        });


    function formatDate(input) {
        var datePart = input.match(/\d+/g),
        year = datePart[0], // get only two digits
        month = datePart[1], day = datePart[2];
        return day + '/' + month + '/' + year;
    }

    // alert(formatDate('2010/01/18'));


    function getAge(dateString) {
        var today = new Date();
        var birthDate = new Date(dateString);
        var age = today.getFullYear() - birthDate.getFullYear();
        var m = today.getMonth() - birthDate.getMonth();
        if (m < 0 || (m === 0 && today.getDate() < birthDate.getDate())) {
            age--;
        }
        return age;
    }

下面是我能想到的最简单、最准确的解决方案:

Date.prototype.getAge = function (date) {
    if (!date) date = new Date();
    return ~~((date.getFullYear() + date.getMonth() / 100
    + date.getDate() / 10000) - (this.getFullYear() + 
    this.getMonth() / 100 + this.getDate() / 10000));
}

下面是一个考虑每年2月29日至2月28日的例子。

Date.prototype.getAge = function (date) {
    if (!date) date = new Date();
    var feb = (date.getMonth() == 1 || this.getMonth() == 1);
    return ~~((date.getFullYear() + date.getMonth() / 100 + 
        (feb && date.getDate() == 29 ? 28 : date.getDate())
        / 10000) - (this.getFullYear() + this.getMonth() / 100 + 
        (feb && this.getDate() == 29 ? 28 : this.getDate()) 
        / 10000));
}

它甚至适用于负年龄!

我有点晚了，但我发现这是计算出生日期的最简单的方法。

希望这能有所帮助。

function init() { writeYears("myage", 0, Age()); } function Age() { var birthday = new Date(1997, 02, 01), //Year, month-1 , day. today = new Date(), one_year = 1000 * 60 * 60 * 24 * 365; return Math.floor((today.getTime() - birthday.getTime()) / one_year); } function writeYears(id, current, maximum) { document.getElementById(id).innerHTML = current; if (current < maximum) { setTimeout(function() { writeYears(id, ++current, maximum); }, Math.sin(current / maximum) * 200); } } init() <span id="myage"></span>