js方法实现通过出生日期获取周岁年龄

/**
strBirthday:指的是出生日期 格式为:"1990-01-01"
*/

function GetAge(strBirthday){
  var returnAge,
  strBirthdayArr=strBirthday.split("-"),
  birthYear = strBirthdayArr[0],
  birthMonth = strBirthdayArr[1],
  birthDay = strBirthdayArr[2],  
  d = new Date(),
  nowYear = d.getFullYear(),
  nowMonth = d.getMonth() + 1,
  nowDay = d.getDate();
  if(nowYear == birthYear){
      returnAge = 0;//同年 则为0周岁
   }
  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
}