function age()
{
    var birthdate = $j('#birthDate').val(); // in   "mm/dd/yyyy" format
    var senddate = $j('#expireDate').val(); // in   "mm/dd/yyyy" format
    var x = birthdate.split("/");    
    var y = senddate.split("/");
    var bdays = x[1];
    var bmonths = x[0];
    var byear = x[2];
    //alert(bdays);
    var sdays = y[1];
    var smonths = y[0];
    var syear = y[2];
    //alert(sdays);

    if(sdays < bdays)
    {
        sdays = parseInt(sdays) + 30;
        smonths = parseInt(smonths) - 1;
        //alert(sdays);
        var fdays = sdays - bdays;
        //alert(fdays);
    }
    else{
        var fdays = sdays - bdays;
    }

    if(smonths < bmonths)
    {
        smonths = parseInt(smonths) + 12;
        syear = syear - 1;
        var fmonths = smonths - bmonths;
    }
    else
    {
        var fmonths = smonths - bmonths;
    }

    var fyear = syear - byear;
    document.getElementById('patientAge').value = fyear+' years '+fmonths+' months '+fdays+' days';
}

我在这里测试的所有答案(大约一半)都认为2000-02-29到2001-02-28是0年，而从2000-02-29到2001-03-01最有可能是1年，即1年零1天。这里有一个getYearDiff函数来修复这个问题。它只适用于d0 < d1:

function getYearDiff(d0, d1) {

    d1 = d1 || new Date();

    var m = d0.getMonth();
    var years = d1.getFullYear() - d0.getFullYear();

    d0.setFullYear(d0.getFullYear() + years);

    if (d0.getMonth() != m) d0.setDate(0);

    return d0 > d1? --years : years;
}

我知道这是一个非常古老的线程，但我想把这个实现放在我写的寻找年龄，我相信这是更准确的。

var getAge = function(year,month,date){
    var today = new Date();
    var dob = new Date();
    dob.setFullYear(year);
    dob.setMonth(month-1);
    dob.setDate(date);
    var timeDiff = today.valueOf() - dob.valueOf();
    var milliInDay = 24*60*60*1000;
    var noOfDays = timeDiff / milliInDay;
    var daysInYear = 365.242;
    return  ( noOfDays / daysInYear ) ;
}

当然，你可以调整它以适应其他获取参数的格式。希望这有助于人们寻找更好的解决方案。

看这个例子，你从这里得到完整的年、月、日信息

function getAge(dateString) {
    var today = new Date();
    var birthDate = new Date(dateString);
    var age = today.getFullYear() - birthDate.getFullYear();
    var m = today.getMonth() - birthDate.getMonth();
    var da = today.getDate() - birthDate.getDate();
    if (m < 0 || (m === 0 && today.getDate() < birthDate.getDate())) {
        age--;
    }
    if(m<0){
        m +=12;
    }
    if(da<0){
        da +=30;
    }
    return age+" years "+ Math.abs(m) + "months"+ Math.abs(da) + " days";
}
alert('age: ' + getAge("1987/08/31"));    
[http://jsfiddle.net/tapos00/2g70ue5y/][1]

短而准确(但不是超级可读):

let age = (bdate, now = new Date(), then = new Date(bdate)) => now.getFullYear() - then.getFullYear() - (now < new Date(now.getFullYear(), then.getMonth(), then.getDate()));

这是我的解决方案，只需要传入一个可解析的日期:

function getAge(birth) {
  ageMS = Date.parse(Date()) - Date.parse(birth);
  age = new Date();
  age.setTime(ageMS);
  ageYear = age.getFullYear() - 1970;

  return ageYear;

  // ageMonth = age.getMonth(); // Accurate calculation of the month part of the age
  // ageDay = age.getDate();    // Approximate calculation of the day part of the age
}