我会去阅读： strong>

  function _calculateAge（birthday）{// birthday is a date 
 var ageDifMs = Date.now（） -  birthday.getTime（）; 
 var ageDate = new Date（ageDifMs）; //从epoch开始的毫秒数
 return Math.abs（ageDate.getUTCFullYear（） -  1970）; 
} 
 

免责声明：这也有精确的问题，所以这也不能完全信任。它可以关闭几个小时，几年或夏令时（取决于时区）。

相反，我建议使用一个库，如果精度非常重要。另外 @Naveens post 可能是最准确的，因为它不依赖于一天中的时间。

基准： http://jsperf.com/birthday-calculation/15

How can I calculate an age in years, given a birth date of format YYYYMMDD? Is it possible using the Date() class?

I am looking for a better solution than the one I am using now:

var dob='19800810';
var year=Number(dob.substr(0,4));
var month=Number(dob.substr(4,2))-1;
var day=Number(dob.substr(6,2));
var today=new Date();
var age=today.getFullYear()-year;
if(today.getMonth()<month || (today.getMonth()==month && today.getDate()<day)){age--;}
alert(age);

I would go for readability:

function _calculateAge(birthday) { // birthday is a date
    var ageDifMs = Date.now() - birthday.getTime();
    var ageDate = new Date(ageDifMs); // miliseconds from epoch
    return Math.abs(ageDate.getUTCFullYear() - 1970);
}

Disclaimer: This also has precision issues, so this cannot be completely trusted either. It can be off by a few hours, on some years, or during daylight saving (depending on timezone).

Instead I would recommend using a library for this, if precision is very important. Also @Naveens post, is probably the most accurate, as it doesn't rely on the time of day.

Benchmarks: http://jsperf.com/birthday-calculation/15