How to achieve select select secondary linkage effect

<li style="margin-right:-5px">一级类目：
                    <select id="mainCategoryId" name="mainCategoryId" class="length_2" onchange="changeCate()">
                        <option value="">---请选择---</option>
                        #foreach($cell in $categories)
                            <option value="$!{cell.id}"  #if($!cell.id ==  $!query.mainCategoryId) selected #end >$!{cell.name}</option>
                        #end
                    </select>
                </li>
                <li style="margin-right:-5px">二级类目：
                    <select class="categoryId" name="categoryId" class="length_2">
                        <option value="">---请选择---</option>
                    </select>
                </li>

function changeCate(){    
 var  mainCategoryId = 
$("#mainCategoryId").find("option:selected").val();   
 if(mainCategoryId == "") {        
 $(".categoryId").empty().append("<option value=&#39;&#39;>---请选择---</option>");        
 return false;
    }    
 $.ajax({       
     url:&#39;/tvtao/video/item/category.htm&#39;,        
     type:"post",        
     dataType:"json",        
     data: {&#39;_tb_token_&#39; : $("input[name=&#39;_tb_token_&#39;]").val(), parantId : mainCategoryId},        
     success: function (data) {            
     console.log(data);            
     $(".categoryId").empty().append("<option value=&#39;&#39;>---请选择---</option>");           
      for(var i = 0, len = data.length; i < len; i++)
            {                
            alert(data[i].id);                
            $(".categoryId").append($("<option value=&#39;" + data[i].id + "&#39;>" + data[i].name + "</option>"));
            }

        }
    });
}