javascript获取2个日期相隔的年份得到年龄的方法

function getAge(birthDate,currentDate){
                  var returnAge;
                  
            var strBirthdayArr=birthDate.split("-");
            var birthYear = strBirthdayArr[0];
            var birthMonth = strBirthdayArr[1];
            var birthDay = strBirthdayArr[2];
            
            var strCurrentDateArr=currentDate.split("-");
            var nowYear = strCurrentDateArr[0];
            var nowMonth = strCurrentDateArr[1];
            var nowDay = strCurrentDateArr[2];
            
            
            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
  }