一：图片预览：
二：js代码如下：
<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=form1><select name=YYYY οnchange="YYYYMM(this.value)"><option value="">年</option></select><select name=MM οnchange="MMDD(this.value)"><option value="">月</option></select><select name=DD><option value="">日</option></select></form><script language="JavaScript">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];//先给年下拉框赋内容var y = new Date().getFullYear();var str = strYYYY.substring(0, strYYYY.length - 9);for (var i = (y-30); i < (y+30); i++) //以今年为准，前30年，后30年{str += "<option value='" + i + "'> " + i + "</option>\r\n";}document.form1.YYYY.outerHTML = str +"</select>";//赋月份的下拉框var str = strMM.substring(0, strMM.length - 9);for (var i = 1; i < 13; i++){str += "<option value='" + i + "'> " + i + "</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); //赋日期下拉框document.form1.DD.value = new Date().getDate();}function YYYYMM(str) //年发生变化时日期发生变化(主要是判断闰平年){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) //月发生变化时日期联动{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) //据条件写日期的下拉框{var s = strDD.substring(0, strDD.length - 9);for (var i=1; i<(n+1); i++)s += "<option value='" + i + "'> " + i + "</option>\r\n";document.form1.DD.outerHTML = s +"</select>";}function IsPinYear(year)//判断是否闰平年{ return(0 == year%4 && (year%100 !=0 || year%400 == 0))}//--></script></body></html>
