select菜单实现二级联动

<span style="white-space:pre">	</span><tr>
                <th>执行人<b>*</b></th>
                <td>
                    <select name="jdcld.ZXDW" id="zxrDw" onchange="zxDwChange()" class="select" style="width:230px">
                        <option value="">选择部门</option>
                    <#if zxrBm??&&zxrBm?size!=0>
                        <#list zxrBm as bm>
                            <option value="${bm['id']}">${bm['mc']}</option>
                        </#list>
                    </#if>
                    </select>
                    <select name="jdcld.ZXRID" id="zxrId" class="select" style="width:230px">
                        <option value="">选择民警</option>
                    </select>
                    <input type="hidden" name="jdcld.ZXRXM"/>
                </td>
<span style="white-space:pre">	</span></tr>

function zxDwChange() {
        var bmid = $("#zxrDw").val();
        alert(bmid);
        $("#zxrId").empty();
        var text = "<option value=''>选择民警</option>";
        $.post("${base}/zfjd/zxrList", {"bmid":bmid}, function(data) {
            if (data != "") {
                var dataArr = eval('(' + data + ')');
                for (var i in dataArr) {
                    text += "<option value='" + dataArr[i].value + "'>" + dataArr[i].title + "</option>";
                }
                if (text == "<option value=''>选择民警</option>") {
                    $("#zxrId").append("<option value=''>选择民警</option>");
                } else
                    $("#zxrId").append(text);
            } else {
                $("#zxrId").append("<option value=''>选择民警</option>");
            }
        });
    }