JS實現根據出生日期得到年齡方法

JavaScript//JS根據出生日期 得到年齡 //參數strBirthday已經是正確格式的2017-12-12這樣的日期字符串 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 則為0歲 
 } 
 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 表示出生日期輸入錯誤 晚于今天 
 } 
 } 
 return returnAge;//返回周歲年齡 }

JavaScript//JS根據出生日期 得到年齡 //參數strBirthday已經是正確格式的2017-12-12這樣的日期字符串 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 則為0歲 
 } 
 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 表示出生日期輸入錯誤 晚于今天 
 } 
 } 

 return returnAge;//返回周歲年齡 }