两个下拉框，选择第一个下拉框，第二个下拉框中的值随着相应的变化！

Question

<script>
function func()
{
  s2.options.length = 0;
  s2.options[0] = new Option(s1.value, s1.value);    
}
</script>
<select id="s1" onchange="func()">
<option>1</option>
<option>2</option>
<option>3</option>
</select><select id="s2">
</select>

Answer 1

http://lucky.myrice.com/javascriptexam/radioforselect.html

Answer 2

<div id=kkk></div>
kkk.inertHTML="<select>你想咋写就咋写</selec>"

Answer 3

举个例子给你看（具体效果见：http://www.aspsky.net/download/index_1.asp?classid=1）
————————————————————
<script language = "JavaScript">//这里建立多级菜单项的值，共53项。
var onecount;
onecount=0;
subcat = new Array();
subcat[0] = new Array("ASP交友聊天","1","1");
subcat[1] = new Array("ASP论坛社区","1","2");
subcat[2] = new Array("ASP搜索链接","1","3");
subcat[3] = new Array("ASP留言计数","1","4");
subcat[4] = new Array("ASP信息管理","1","5");
subcat[5] = new Array("ASP教程下载","1","6");
subcat[6] = new Array("ASP电子商务","1","7");
subcat[7] = new Array("精品组件","3","8");
subcat[8] = new Array("ASP工具软件","1","9");
subcat[9] = new Array("ASP另类其他","1","10");
subcat[10] = new Array("PHP广告管理","2","11");
subcat[11] = new Array("PHP聊天程序","2","12");
subcat[12] = new Array("PHP论坛程序","2","13");
subcat[13] = new Array("PHP新闻栏目","2","14");
subcat[14] = new Array("PHP访客留言","2","15");
subcat[15] = new Array("PHP数据管理","2","16");
subcat[16] = new Array("PHP开发工具","2","17");
subcat[17] = new Array("PHP另类其他","2","18");
subcat[18] = new Array("浏览器组件","3","19");
subcat[19] = new Array("消息新闻组件","3","20");
subcat[20] = new Array("论坛社区组件","3","21");
subcat[21] = new Array("日历时间组件","3","22");
subcat[22] = new Array("聊天通讯组件","3","23");
subcat[23] = new Array("内容管理组件","3","24");
subcat[24] = new Array("转换类型组件","3","25");
subcat[25] = new Array("数据库组件","3","26");
subcat[26] = new Array("电子邮件组件","3","27");
subcat[27] = new Array("文件处理组件","3","28");
subcat[28] = new Array("表格处理组件","3","29");
subcat[29] = new Array("图像图表组件","3","30");
subcat[30] = new Array("HTML生成组件","3","31");
subcat[31] = new Array("多媒体组件","3","32");
subcat[32] = new Array("网络功能组件","3","33");
subcat[33] = new Array("程序工具组件","3","34");
subcat[34] = new Array("安全加密组件","3","35");
subcat[35] = new Array("购物商业组件","3","36");
subcat[36] = new Array("用户界面组件","3","37");
subcat[37] = new Array("用户管理组件","3","38");
subcat[38] = new Array("站点导航组件","3","39");
subcat[39] = new Array("XML技术组件","3","40");
subcat[40] = new Array("另类其他组件","3","41");
subcat[41] = new Array("Jsp教程","4","42");
subcat[42] = new Array("JSP论坛社区","4","43");
subcat[43] = new Array("JSP电子商务","4","44");
subcat[44] = new Array("JSP信息管理","4","45");
subcat[45] = new Array("JSP广告管理","4","46");
subcat[46] = new Array("JSP留言日历","4","47");
subcat[47] = new Array("JSP聊天投票","4","48");
subcat[48] = new Array("JSP统计游戏","4","49");
subcat[49] = new Array("动网论坛下载","5","50");
subcat[50] = new Array("动网论坛补丁","5","51");
subcat[51] = new Array("动网论坛插件","5","52");
subcat[52] = new Array("动网论坛Skin","5","53");
onecount=53;function changelocation(locationid)//这里建立改变下拉框的函数changelocation()
    {
    document.myform.Nclassid.length = 0; 
    var locationid=locationid;
    var i;
    for (i=0;i < onecount; i++)
        {
            if (subcat[i][1] == locationid)
            { 
                document.myform.Nclassid.options[document.myform.Nclassid.length] = new Option(subcat[i][0], subcat[i][2]);
            }        
        }
    }    
</script>//以下内容是调用<select name="classid" onChange="changelocation(document.myform.classid.options[document.myform.classid.selectedIndex].value)" size="1">//这是第一级
<option selected value="">未指定条件</option>
        <option value="1">ASP下载</option>
        <option value="2">PHP下载</option>
        <option value="3">ASP组件</option>
        <option value="4">JSP下载</option>
        <option value="5">动网论坛专区</option>
       </select> 
    <select name="Nclassid">                  //这是第二级
        <option selected value="">未指定条件</option>
    </select>

Answer 4

写个函数吧!用onChange事件触发
function clk(v){
var obj = document.all.lst2;
if (v==0) { obj.length=0; obj.disabled=false; initlst(obj,4);return }
if (v==1) { obj.length=0; obj.disabled=false; initlst(obj,3); return }
if (v==2) { obj.length=0; obj.disabled=false; initlst(obj,2); return }
if (v==3) {obj.length=0;  obj.disabled=false; initlst(obj,5); return }
}
function initlst(o,v){
for(var i=1;i<v+1;i++){
if(v==4){
o.options[0]=new Option("工程开发部",1);
o.options[1]=new Option("管理部",1);
o.options[2]=new Option("营销部",1);
}
if(v==3){
    o.options[0]=new Option("工程开发部",1);
o.options[1]=new Option("南昌管理部",1);
o.options[2]=new Option("南昌营销部",1);
}
if(v==2){
    o.options[0]=new Option("仪征工程管理部",1);
o.options[1]=new Option("仪征客户服务部",1);
}
if(v==5){
    o.options[0]=new Option("荆州工程管理部",1);
o.options[1]=new Option("荆州客户服务部",1);
}
}}

Answer 5

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<title>测试页面</title>
<script language="JavaScript" defer>
var arr=["aa","bb","cc","dd"];
var arr2=[["aa1","aa2"],["bb1","bb2"],["cc1","cc2","cc3","cc4"],["dd1","dd2"]];
for(i=0;i<arr.length;i++)
{
  form1.t1.options[i] = new Option(arr[i]);
}
function checkit(num)
{
form1.t2.innerHTML="";
for(i=0;i<arr2[num].length;i++)
{
  form1.t2.options[i] = new Option(arr2[num][i]);
}
}
</script>
</head><body onLoad="checkit(0)">
<form name="form1" method="post" action="">
<select name="t1" id="t1" onChange="checkit(selectedIndex)">
</select>
<select name="t2" id="t2">
</select>
</form>
</body>
</html>