javascript根据生日计算年龄

<SCRIPT LANGUAGE="JavaScript">
<!--
var birthday=new Date("1983-12-31".replace(/-/g, "\/"));
var d=new Date();
var age = d.getFullYear()-birthday.getFullYear()-((d.getMonth()<birthday.getMonth()|| d.getMonth()==birthday.getMonth() && d.getDate()<birthday.getDate())?1:0);
alert(age);
//-->
</SCRIPT>