求代码，来解决两个下拉框的联动

我有两个下拉框，分别为：
下拉框一
<select onchange="A(this)" name="STy1" id="STy1" size="1"><option value="sn" selected="true">Family/Last Name</option><option value="cn">Full Name</option><option value="id">ID</option></select>
和下拉框二
<select name="SLk1" id="SLk1" size="1"><option value="OBW">That Begins With</option><option value="OOS">That Contains</option><option value="OEM">That Equals</option></select>我现在想知道怎么写js的function A(obj)，来实现以下功能。
1）选中下拉框一的ID，下拉框二中就只剩“That Equals”选项。
2）选中下拉框一的“Family/Last Name”或者“Full Name”，下拉框二中所有选项都可选，默认选中“That Begins With”。非常感谢！

解决方案 »

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<select onchange="A(this)" name="STy1" id="STy1" size="1">
<option value="sn" selected="true">Family/Last Name</option>
<option value="cn">Full Name</option>
<option value="id">ID</option>
</select>
<select name="SLk1" id="SLk1" size="1">
<option value="OBW">That Begins With</option>
<option value="OOS">That Contains</option>
<option value="OEM">That Equals</option></select>
<script type="text/javascript">
    var opt = [];
    function A(obj) {
        var sel = document.getElementById('SLk1');
        if (obj.value == 'id') {
            if (opt.length == 0) { opt[0] = sel.options[0]; opt[1] = sel.options[1]; } //存储起来，IE不支持option的style="display:none"
            //删除1,2项
            sel.removeChild(sel.options[0]);
            sel.removeChild(sel.options[0]);
        }
        else if (sel.options.length == 1) { //重新添加1,2项
            sel.insertBefore(opt[0],sel.options[0]);
            sel.insertBefore(opt[1], sel.options[1]);
            sel.selectedIndex = 0;
        }
    }
</script>
<html>
<head>
    <title>demo</title>
</head>
<body>
    <select onchange="A(this)" name="STy1" id="STy1" size="1">
        <option value="sn" selected="selected" show="OBW,OOS,OEM" defvalue="OBW">Family/Last Name</option>
        <option value="cn" show="OBW,OOS,OEM" defvalue="OBW">Full Name</option>
        <option value="id" show="OEM" defvalue="OEM">ID</option>
    </select>
    <select name="SLk1" id="SLk1" size="1">
        <option value="OBW">That Begins With</option>
        <option value="OOS">That Contains</option>
        <option value="OEM">That Equals</option>
    </select>
    <script type="text/javascript">
        var Ori = {
            STy1: "STy1",
            SLk1Id: "SLk1",
            SLk1: [],
            Init: function() {
                var obj = document.getElementById(this.SLk1Id);
                var list = [];
                if (obj) {
                    for (var i = 0; i < obj.options.length; i++) {
                        list[i] = { text: obj.options[i].text, value: obj.options[i].value };
                    }
                    this.SLk1 = list;
                    A(document.getElementById(this.STy1));
                }
            },
            Show: [],
            ShowDefIndex: 0,
            SetShow: function() {
                var obj = document.getElementById(this.SLk1Id);
                if (obj) {
                    obj.options.length = 0;
                    for (var i = 0; i < this.Show.length; i++) {
                        obj.options[i] = new Option(this.Show[i].text, this.Show[i].value);
                    }
                    obj.selectedIndex = this.ShowDefIndex;
                }
            }
        };
        function A(obj) {
            var show = obj.options[obj.selectedIndex].getAttribute("show");
            var defvalue = obj.options[obj.selectedIndex].getAttribute("defvalue")||"";
            if (show) {
                Ori.ShowDefIndex = 0;
                show = show.split(",");
                Ori.Show.length = 0;
                var index = 0;
                for (var i = 0; i < show.length; i++) {
                    for (var j = 0; j < Ori.SLk1.length; j++) {
                        if (Ori.SLk1[j].value == show[i]) {
                            if (defvalue == show[i]) {Ori.ShowDefIndex = index; }
                            Ori.Show[index] = { text: Ori.SLk1[j].text, value: Ori.SLk1[j].value };
                            index++;
                            continue;
                        }
                    }
                }
                Ori.SetShow();
            }
        }
        window.onload = function() {
            Ori.Init();
        };
    </script>
</body>
</html>
以前用的时候写了一个,拿来改了下,可以满足楼主的需求
下面的方法可以保留下拉菜单的任意项，或者选中任意项<body>
<select  name="STy1" id="STy1" size="1">
<option value="sn" selected="true">Family/Last Name</option>
<option value="cn">Full Name</option>
<option value="id">ID</option>
</select>
<select name="SLk1" id="SLk1" size="1">
<option value="OBW">That Begins With</option>
<option value="OOS">That Contains</option>
<option value="OEM">That Equals</option>
</select> <script type="text/javascript">
(function(){

//存储可变下拉框选项
var opt = [],

//存储可变下拉框对象
sel = document.getElementById('SLk1');

//将可变下拉框中的选项存入数组中
(function(){
var i = 0;
while (opt.length != sel.length){
opt[i] = sel.options[i];
i++;
}
})();

//当选中项发生变化时，调用处理函数
document.getElementById("STy1").onchange = function(){
A(this, 2,1);
};

//obj下拉对象，n为选择"id"后的剩余项下标，selectedN为被选中项下标（下标从0开始）
function A(obj,n,selectedN) {

//选中项为Id是，将所有项删除，添加剩余项
if (obj.value == 'id') {

while(sel.length){
sel.removeChild(sel.options[0]);
}
sel.options[0] = opt[n];

}

//加载所有项
else if(sel.length == 1){
sel.removeChild(sel.options[0]);

(function(){

var i = 0;
while(sel.length != opt.length){
sel.options[i] = opt[i];
i++;
}
})();

sel.options[selectedN].selected = "selected";
}

//选中项
else{
sel.options[selectedN].selected = "selected";
}
}
})();
</script>
</body>
[Quote=引用 3 楼  的回复:]上个帖子里面两处兼容性没有处理：
sel.options[0] = opt[n]; =》 sel.appendChild(opt[n]);
sel.options[i] = opt[i]; =》 sel.appendChild(opt[i]);
function setfillGroupId(val)
{
$.ajax({
   type: "post",
    url: "/yoblhtjfx/queryArea.action",
    data: "parm="+val+"&jsoncallback=?",
    dataType: "json",
    success: function(json){
    var list = json.list;
    $("#inUnitAreaId").empty();
    $("#inUnitAreaId").prepend("<option value=''>è¯·éæ©</option>");
for(var i=0;i<list.length;i++)
{
    $("#inUnitAreaId").append("<option value='"+list[i][0]+"'>"+list[i][1]+"</option>");
    }
    }

   });
}给你一个我的，里面的乱码是没改字符集，不影响你，相信你看的懂，只不过我去后台查了一遍数据，你的就简单啦，不用查直接写上去就行了，你说的选中的那个直接加个selected属性就行了，记得引入jquery的js。