<form name="birthdayForm" id="birthdayForm" method="get" action="./birthday.cgi">
誕生年:<input type="text" size="16" name="birthYear" id="birthYear"><br>
<input type="button" value="西暦に変換" id="toSeireki">
<input type="button" value="和暦に変換" id="toWareki">
</form>
(function(){
if (window.addEventListener) window.addEventListener("load", setConvert, true);
if (window.attachEvent) window.attachEvent("onload", setConvert);
function setConvert(){
document.getElementById("toSeireki").onclick = function(){
var year = document.getElementById("birthYear").value;
document.getElementById("birthYear").value = wareki_to_seireki(year);
}
document.getElementById("toWareki").onclick = function(){
var year = document.getElementById("birthYear").value;
document.getElementById("birthYear").value = seireki_to_wareki(year);
}
function seireki_to_wareki(y){
y = parseInt(y);
if (y > 1988) return "平成"+(y - 1988);
if (y > 1925) return "昭和"+(y - 1925);
if (y > 1911) return "大正"+(y - 1911);
if (y > 1867) return "明治"+(y - 1867);
return y;
}
function wareki_to_seireki(str){
var m = str.substring(0,2);
var y = parseInt(str.substring(2,str.length));
if ((m == "平成") && (y > 0) && (y < 50)) return 1988 + y;
if ((m == "昭和") && (y > 0) && (y < 65)) return 1925 + y;
if ((m == "大正") && (y > 0) && (y < 16)) return 1911 + y;
if ((m == "明治") && (y > 0) && (y < 46)) return 1867 + y;
return str;
}
}
})();