JS根據生日算歲數

function parseDate(str){
    if(str.match(/^\d{4}[\-\/\s+]\d{1,2}[\-\/\s+]\d{1,2}$/)){
        return new Date(str.replace(/[\-\/\s+]/i,'/'));
    }
    else if(str.match(/^\d{8}$/)){
        return new Date(str.substring(0,4)+'/'+str.substring(4,6)+'/'+str.substring(6));
    }
    else{
        return ('時間轉換發生錯誤！');
    }
}

function GetAgeByBrithday(birthday){
 var age=-1;
 var today=new Date();
 var todayYear=today.getFullYear();
 var todayMonth=today.getMonth()+1;
 var todayDay=today.getDate();
 var birthday=parseDate(birthday);
 if(parseDate(birthday)!='時間轉換發生錯誤！')
 {
 birthdayYear=birthday.getFullYear();
 birthdayMonth=birthday.getMonth();
 birthdayDay=birthday.getDate();
 if(todayYear-birthdayYear<0)
 {
        alert("出生日期選擇錯誤!");
 }
 else
 {
        if(todayMonth*1-birthdayMonth*1<0)
        {
               age = (todayYear*1-birthdayYear*1)-1;
        }
        else
        {
               if(todayDay-birthdayDay>=0)
               {//alert(thisDay+'-'+brithd+"_ddd");
                      age = (todayYear*1-birthdayYear*1);
               }
               else
               {
                      age = (todayYear*1-birthdayYear*1)-1;
               }
        }
 }
 return age*1;
 }
 else
 {
   return -1;
 }
}