<!-- 要实现此效果需要 1 个步骤： -->
<!-- 第 1 步： -->
<!-- 把下面的代码加到<BODY></BODY>区域中： -->
<form name=f1>
<select name=year size=1 onchange="showmonth();showday()">
<script>
var yearbegin=1900,yearend=2005;
document.write("<option value=''selected>请选择年份...</option>")
for(var i=yearbegin;i<=yearend;i++){
document.write ("<option value="+i+">"+i+"</option>")
}
</script>
</select>
<select name=month size=1 onchange="showday();">
<option value="">请选择月份...</option>
</select>
<select name=day size=1>
<option value="">请选择日期...</option>
</select>
</form>
<script>
var elYear=eval(document.f1.year)
var elMonth=eval(document.f1.month);
function showmonth(){
if(elYear.value!=""){
for(var i=0;i<12;i++){
elMonth.options.add(new Option(i+1, i+1));
}
}
}
function showday(){
var elDay=eval(document.f1.day);
if(elMonth.value!="" && elYear.value!=""){
elDay.length=0;
for(var i=0;i<28;i++){
elDay.options.add(new Option(i+1, i+1));
}
if(elMonth.value!="2"){
elDay.options.add(new Option(29, 29));
elDay.options.add(new Option(30, 30));
}
switch(elMonth.value){
case "1":
case "3":
case "5":
case "7":
case "8":
case "10":
case "12":{
elDay.options.add(new Option(31, 31));
}
case "2":{
var nYear=elYear.value;
if(nYear%400==0 || nYear%4==0 && nYear%100!=0)elDay.options.add(new Option(29, 29));
}
}
}
}
</script>