JS实现根据出生日期得到年龄方法

JavaScript//JS根据出生日期 得到年龄                 //参数strBirthday已经是正确格式的2017-12-12这样的日期字符串  function jsGetAge(strBirthday)  {         
    var returnAge;  
    var strBirthdayArr=strBirthday.split("-");  
    var birthYear = strBirthdayArr[0];  
    var birthMonth = strBirthdayArr[1];  
    var birthDay = strBirthdayArr[2];  
    var d = new Date();  
    var nowYear = d.getYear();  
    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  }

JavaScript//JS根据出生日期 得到年龄                 //参数strBirthday已经是正确格式的2017-12-12这样的日期字符串  function jsGetAge(strBirthday)  {         
    var returnAge;  
    var strBirthdayArr=strBirthday.split("-");  
    var birthYear = strBirthdayArr[0];  
    var birthMonth = strBirthdayArr[1];  
    var birthDay = strBirthdayArr[2];  

    var d = new Date();  
    var nowYear = d.getYear();  
    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  }