动态生成年月日下拉选择框

 <form id="form1"  action ="" onload="YYYYMMDDstart(document.form1,document.form1.SYear,document.form1.SMonth,document.form1.SDay)">
    <script type="text/javascript"language ="javascript" >
   function YYYYMMDDstart(form,year,month,day)
   {
      MonHead = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];

      //先给年下拉框赋内容
     var y = new Date().getFullYear();
        for (var i = (y-3); i < (y+5); i++) //以今年为准，前30年，后30年
          year.options.add(new Option(i,i));

        //赋月份的下拉框
         for (var i = 1; i < 13; i++)
        month.options.add(new Option(i,i));

         year.value = y;
      month.value = new Date().getMonth() + 1;
      var n = MonHead[new Date().getMonth()];
       if (new Date().getMonth() ==1 && IsPinYear(year.options[year.selectedIndex].value)) n++;
     writeDay(n,day); //赋日期下拉框Author:meizz
day.value = new Date().getDate();
}
function YYYYDD(str,month,day) //年发生变化时日期发生变化(主要是判断闰平年)
{
var MMvalue = month.options[month.selectedIndex].value;
if (MMvalue == "" ){ var e = day; optionsClear(e); return;}
var n = MonHead[MMvalue - 1];
if (MMvalue ==2 && IsPinYear(str)) n++;
writeDay(n,day)
}