html年月日下拉联动菜单 年月日三下拉框联动

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<html><head><title>年月日三下拉框联动</title><meta http-equiv='Content-Type' content='text/html; charset=gb2312'></head><body><form name="reg_testdate">  <select name="YYYY" onchange="YYYYDD(this.value)">    <option value="">请选择 年</option>  </select>  <select name="MM" onchange="MMDD(this.value)">    <option value="">选择 月</option>  </select>  <select name="DD">    <option value="">选择 日</option>  </select></form><script language="JavaScript"><!--      function YYYYMMDDstart()      {              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-30); i < (y+30); i++) //以今年为准,前30年,后30年                      document.reg_testdate.YYYY.options.add(new Option(" "+ i +"", i));                  //赋月份的下拉框              for (var i = 1; i < 13; i++)                      document.reg_testdate.MM.options.add(new Option(" " + i + "", i));                  document.reg_testdate.YYYY.value = y;              document.reg_testdate.MM.value = new Date().getMonth() + 1;              var n = MonHead[new Date().getMonth()];              if (new Date().getMonth() ==1 && IsPinYear(YYYYvalue)) n++;                   writeDay(n); //赋日期下拉框Author:meizz              document.reg_testdate.DD.value = new Date().getDate();      }      if(document.attachEvent)          window.attachEvent("onload", YYYYMMDDstart);      else          window.addEventListener('load', YYYYMMDDstart, false);      function YYYYDD(str) //年发生变化时日期发生变化(主要是判断闰平年)      {              var MMvalue = document.reg_testdate.MM.options[document.reg_testdate.MM.selectedIndex].value;              if (MMvalue == ""){ var e = document.reg_testdate.DD; optionsClear(e); return;}              var n = MonHead[MMvalue - 1];              if (MMvalue ==2 && IsPinYear(str)) n++;                   writeDay(n)      }      function MMDD(str)   //月发生变化时日期联动      {           var YYYYvalue = document.reg_testdate.YYYY.options[document.reg_testdate.YYYY.selectedIndex].value;           if (YYYYvalue == ""){ var e = document.reg_testdate.DD; optionsClear(e); return;}           var n = MonHead[str - 1];           if (str ==2 && IsPinYear(YYYYvalue)) n++;          writeDay(n)      }      function writeDay(n)   //据条件写日期的下拉框      {              var e = document.reg_testdate.DD; optionsClear(e);              for (var i=1; i<(n+1); i++)                   e.options.add(new Option(" "+ i + "", i));      }      function IsPinYear(year)//判断是否闰平年      {     return(0 == year%4 && (year%100 !=0 || year%400 == 0));}      function optionsClear(e)      {           e.options.length = 1;      }      //--></script></body></html>