使用js+jquery实现无限极联动

<div id="select" >
    <select name="category_1" id="category_1" onChange="change('category_1');">
        <option>请选择分类</option>
        <!-- {foreach from=$galleryCategory item=category} -->
            <option value="{$category.id}">{$category.category_name}</option>
        <!-- {/foreach} -->   
    </select>
</div>

$sql = " select * from yl_gallery_category where pid = 0";
$galleryCategory = $db->query($sql);
$smarty->assign("galleryCategory",$galleryCategory);

var str = val; //select的id
    var num; //当前级数
    var id; // 分类id
    num = str.substr(9,10);
    //alert(num);
    var nownum = parseInt(num)+1; // 将字符串转换为数字
    id = $("#"+str+"").val();
    var r = /^[1-9]+[0-9]*]*$/;　//正整数
    if (!r.test(id)) {
        //清空过时的选项
        $("select").each(function(index){
            if(index+1 > num) {
                $(this).remove();
            }
        })

        return false;
    }
    var url = 'gallery.php?act=category&pid='+id;
    $.ajax({
        type: "POST",
        cache: false,
        url: url,
        datatype : 'json',
        timeout : 3000,
        success: function(result){
            if ( result != 0) {   
                var html = "<select name=category_"+nownum+"     id=category_"+nownum+"  onChange=change('category_"+nownum+"'); >";
                html += "<option>请选择分类 </option>";
                var datas = eval(result);
                $.each(datas, function(i,val){     
                    html += "<option value='"+val.id+"' >"+val.category_name+"</option>";
                });  
                html += "</select>";

                //清空过时的选项
                $("select").each(function(index){
                    if(index+1 > num) {
                        $(this).remove();
                    }
                })

                $("#select").append(html);
            } else {
　　　　　　　　　　//清空过时的选项
                $("select").each(function(index){
                    if(index+1 > num) {
                        $(this).remove();
                    }
                })　　　　　　　}

        },
        error: false
    });

}

$sql = " select * from yl_gallery_category where pid = " .$pid;
    $res = $db->query($sql);
    if (empty($res)) {
        $res = 0;
    }
    echo json_encode($res);