現在世界通用的公歷（陽歷）也經過一個長期演變的過程。我們先看，公歷每個月的日數是固定的："七前單大，八后雙大"。也就是說，一、三、五、七、八、十、臘月（十二月）是31天，四、六、九、十一月是30天，只有二月，平年28天，閏年29天。
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
<title></title>
</head>
<body>
<form id="form1" runat="server">
<div>
<select name=YYYY id="YYYY" onchange="YYYYMM(this.value)">
<option value="">選擇 年</option>
</select>
<select name=MM id="MM" onchange="MMDD(this.value)">
<option value="">選擇 月</option>
</select>
<select name=DD id="DD">
<option value="">選擇 日</option>
</select>
</div>
<asp:HiddenField ID="hfValue" runat="server" />
<asp:Button ID="btnSave" runat="server" Text="保存" onclick="btnSave_Click" />
</form>
</body>
</html>
<script language="JavaScript">
<!--
function getValue() {
var year = document.getElementById("YYYY").options[document.getElementById("YYYY").selectedIndex].value;
var month = document.getElementById("MM").options[document.getElementById("MM").selectedIndex].value;
var day = document.getElementById("DD").options[document.getElementById("DD").selectedIndex].value;
document.getElementById("hfValue").value = year+"-"+month+"-"+day;
}
window.onload=function() {
strYYYY = document.form1.YYYY.outerHTML;
strMM = document.form1.MM.outerHTML;
strDD = document.form1.DD.outerHTML;
MonHead = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];
//先給年下拉框賦內容
var y = new Date().getFullYear();
var str = strYYYY.substring(0, strYYYY.length - 9);
for (var i = (y - 80); i < (y + 2); i++) //以今年為準，前30年，后30年
{
str += "<option value='" + i + "'> " + i + " 年" + "</option>/r/n";
}
document.form1.YYYY.outerHTML = str + "</select>";
//賦月份的下拉框
var str = strMM.substring(0, strMM.length - 9);
for (var i = 1; i < 13; i++) {
str += "<option value='" + i + "'> " + i + " 月" + "</option>/r/n";
}
document.form1.MM.outerHTML = str + "</select>";
document.form1.YYYY.value = y;
document.form1.MM.value = new Date().getMonth() + 1;
var n = MonHead[new Date().getMonth()];
if (new Date().getMonth() == 1 && IsPinYear(YYYYvalue)) n++;
writeDay(n); //賦日期下拉框
document.form1.DD.value = new Date().getDate();
}
function YYYYMM(str) //年發生變化時日期發生變化(主要是判斷閏平年)
{
var MMvalue = document.form1.MM.options[document.form1.MM.selectedIndex].value;
if (MMvalue == "") {
DD.outerHTML = strDD;
return;
}
var n = MonHead[MMvalue - 1];
if (MMvalue == 2 && IsPinYear(str)) n++;
writeDay(n)
}
function MMDD(str) //月發生變化時日期聯動
{
var YYYYvalue = document.form1.YYYY.options[document.form1.YYYY.selectedIndex].value;
if (str == "") {
DD.outerHTML = strDD;
return;
}
var n = MonHead[str - 1];
if (str == 2 && IsPinYear(YYYYvalue)) n++;
writeDay(n)
}
function writeDay(n) //據條件寫日期的下拉框
{
var s = strDD.substring(0, strDD.length - 9);
for (var i = 1; i < (n + 1); i++) s += "<option value='" + i + "'> " + i + " 日" +
"</option>/r/n";
document.form1.DD.outerHTML = s + "</select>";
}
function IsPinYear(year) //判斷是否閏平年
{
return (0 == year % 4 && (year % 100 != 0 || year % 400 == 0))
}
//-->
</script>
namespace WebApplication1
{
public partial class WebForm1 : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
btnSave.Attributes.Add("onclick", "getValue()");
}
protected void btnSave_Click(object sender, EventArgs e)
{
Response.Write(hfValue.Value);
}
}
}
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