Javascript通过日期获取用户的年龄

<script type="text/javascript">
	function jsGetAge(strBirthday) {
		var returnAge;
		var strBirthdayArr = strBirthday.split("-");
		var birthYear = strBirthdayArr[0];
		var birthMonth = strBirthdayArr[1];
		var birthDay = strBirthdayArr[2];
		d = new Date();
		var nowYear = d.getFullYear();
		alert(nowYear);
		var nowMonth = d.getMonth() + 1;
		var nowDay = d.getDate();
		if (nowYear == birthYear) {
			returnAge = 0;//同年 则为0岁
		} else {
			var ageDiff = nowYear - birthYear; //年之差
			if (ageDiff > 0) {
				if (nowMonth == birthMonth) {
					var dayDiff = nowDay - birthDay;//日之差
					if (dayDiff < 0) {
						returnAge = ageDiff - 1;
					} else {
						returnAge = ageDiff;
					}
				} else {
					var monthDiff = nowMonth - birthMonth;//月之差
					if (monthDiff < 0) {
						returnAge = ageDiff - 1;
					} else {
						returnAge = ageDiff;
					}
				}
			} else {
				returnAge = -1;//返回-1 表示出生日期输入错误 晚于今天
			}
		}
		return returnAge;//返回周岁年龄
	}
	function age() {
		var ag = jsGetAge("1988-4-8");
	}
</script>