JS:根据出生日期 得到年龄

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  }