<!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"); //包含所有大月的數(shù)組
var month_small = new Array("4","6","9","11"); //包含所有小月的數(shù)組 

//頁(yè)面加載時(shí)調(diào)用的初始化select控件的option的函數(shù)
function init()
{
  var select_year = document.getElementById("year"); //獲取id為"year"的下拉列表框
  var select_month = document.getElementById("month"); //獲取id為"month"的下拉列表框
  var select_day = document.getElementById("day"); //獲取id為"day"的下拉列表框
  
  //將年份選項(xiàng)初始化，從1980到2000
  for(var i = 1980; i <= 2000; i++)
  {
    select_year_option = new Option(i, i);
    select_year.options.add(select_year_option);
  }
  
  //將月份選項(xiàng)初始化，從1到12
  for(var i = 1; i <= 12; i++)
  {
    select_month_option = new Option(i, i);
    select_month.options.add(select_month_option);
  }
  
  //調(diào)用swap_day函數(shù)初始化日期  
  swap_day();
}
//判斷數(shù)組array中是否包含元素obj的函數(shù)，包含則返回true，不包含則返回false
function array_contain(array, obj)
{
  for (var i = 0; i < array.length; i++)
  {
    if (array[i] === obj)
    {
      return true;
    }
  }
  return false;
}

//根據(jù)年份和月份調(diào)整日期的函數(shù)
function swap_day()
{
  var select_year = document.getElementById("year"); //獲取id為"year"的下拉列表框
  var select_month = document.getElementById("month"); //獲取id為"month"的下拉列表框
  var select_day = document.getElementById("day"); //獲取id為"day"的下拉列表框
  
  select_day.options.length = 0; //在調(diào)整前先清空日期選項(xiàng)里面的原有選項(xiàng)
  var month = select_month.options[select_month.selectedIndex].value; //獲取被選中的月份month
  
  //如果month被包含在month_big數(shù)組中，即被選中月份是大月，則將日期選項(xiàng)初始化為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數(shù)組中，即被選中月份是小月，則將日期選項(xiàng)初始化為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為2，即被選中的月份是2月，則調(diào)用initFeb()函數(shù)來(lái)初始化日期選項(xiàng)
  else
  {
    initFeb();   
  }
}
//判斷年份year是否為閏年，是閏年則返回true，否則返回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;
}

//根據(jù)年份是否閏年來(lái)初始化二月的日期選項(xiàng)
function initFeb()
{
  var select_year = document.getElementById("year"); //獲取id為"year"的下拉列表框
  var select_day = document.getElementById("day"); //獲取id為"day"的下拉列表框
  var year = parseInt(select_year.options[select_year.selectedIndex].value); //獲取被選中的年份并轉(zhuǎn)換成Int
  
  //如果是閏年，則將日期選項(xiàng)初始化為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);
    }
  }
  
  //如果不是閏年，則將日期選項(xiàng)初始化為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>

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