常用js

/****************************************************************
* 機　能： 通过输入的年月日，在js算年龄
****************************************************************/
function autoAge(){

var retval = true;
var year = document.getElementById("year").value;
var month = document.getElementById("month").value;
var day = document.getElementById("day").value;
var yearObj=document.getElementById("year");
if(year<1900){
// alert("不適切な文字が入力されています。");
//yearObj.focus();
return false;
}
var date = new Date(year,(parseInt(month,10) -1)+"",day);
if(parseInt(year,10) >= 1900　&& parseInt(year,10) < 2000){
year = year % 1900;
}
retval = date.getYear() == parseInt(year,10)
&& date.getMonth() == (parseInt(month,10) -1)
&& date.getDate() == parseInt(day);
if (retval == false){
//alert("正しい生年月日を入力してください。");
//yearObj.focus();
return false;
}
var today = new Date();

year = date.getFullYear();
curyear = today.getFullYear();
curmonth = today.getMonth() + 1;
curday = today.getDate();

adjust = (parseInt(curmonth*100) + parseInt(curday)) - (parseInt(month*100) + parseInt(day));
gap = curyear - year;

if (adjust < 0) gap = gap -1;
if (gap < 18){
alert("年齢が１８歳以上で入力されていません。");
yearObj.value="";
yearObj.focus();
return false;
}
document.staffForm.age.value = gap;
}