<!doctype html>
<html>
<head>
<title>年月日</title>
</head>
<body onLoad="init()">
<select id="year" onChange="swap_day()"></select>年
<select id="month" onChange="swap_day()"></select>月
<select id="day"></select>日
</body>
<script>
var month_big = new Array("1","3","5","7","8","10","12"); //包含所有大月的数组
var month_small = new Array("4","6","9","11"); //包含所有小月的数组
//页面加载时调用的初始化select控件的option的函数
function init()
{
var select_year = document.getElementById("year"); //获取id为"year"的下拉列表框
var select_month = document.getElementById("month"); //获取id为"month"的下拉列表框
var select_day = document.getElementById("day"); //获取id为"day"的下拉列表框
//将年份选项初始化，从1980到2000
for(var i = 1980; i <= 2000; i++)
{
select_year_option = new Option(i, i);
select_year.options.add(select_year_option);
}
//将月份选项初始化，从1到12
for(var i = 1; i <= 12; i++)
{
select_month_option = new Option(i, i);
select_month.options.add(select_month_option);
}
//调用swap_day函数初始化日期
swap_day();
}
//判断数组array中是否包含元素obj的函数，包含则返回true，不包含则返回false
function array_contain(array, obj)
{
for (var i = 0; i < array.length; i++)
{
if (array[i] === obj)
{
return true;
}
}
return false;
}
//根据年份和月份调整日期的函数
function swap_day()
{
var select_year = document.getElementById("year"); //获取id为"year"的下拉列表框
var select_month = document.getElementById("month"); //获取id为"month"的下拉列表框
var select_day = document.getElementById("day"); //获取id为"day"的下拉列表框
select_day.options.length = 0; //在调整前先清空日期选项里面的原有选项
var month = select_month.options[select_month.selectedIndex].value; //获取被选中的月份month
//如果month被包含在month_big数组中，即被选中月份是大月，则将日期选项初始化为31天
if(array_contain(month_big, month))
{
for(var i = 1; i <= 31; i++)
{
select_day_option = new Option(i, i);
select_day.options.add(select_day_option);
}
}
//如果month被包含在month_small数组中，即被选中月份是小月，则将日期选项初始化为30天
else if(array_contain(month_small, month))
{
for(var i = 1; i <= 30; i++)
{
select_day_option = new Option(i, i);
select_day.options.add(select_day_option);
}
}
//如果month为2，即被选中的月份是2月，则调用initFeb()函数来初始化日期选项
else
{
initFeb();
}
}
//判断年份year是否为闰年，是闰年则返回true，否则返回false
function isLeapYear(year)
{
var a = year % 4;
var b = year % 100;
var c = year % 400;
if( ( (a == 0) && (b != 0) ) || (c == 0) )
{
return true;
}
return false;
}
//根据年份是否闰年来初始化二月的日期选项
function initFeb()
{
var select_year = document.getElementById("year"); //获取id为"year"的下拉列表框
var select_day = document.getElementById("day"); //获取id为"day"的下拉列表框
var year = parseInt(select_year.options[select_year.selectedIndex].value); //获取被选中的年份并转换成Int
//如果是闰年，则将日期选项初始化为29天
if(isLeapYear(year))
{
for(var i = 1; i <= 29; i++)
{
select_day_option = new Option(i, i);
select_day.options.add(select_day_option);
}
}
//如果不是闰年，则将日期选项初始化为28天
else
{
for(var i = 1; i <= 28; i++)
{
select_day_option = new Option(i, i);
select_day.options.add(select_day_option);
}
}
}
</script>
</html>
