不绑架输入--document.getElementById("linkage_"+id_type+"_echo").value="";--联动

 <script>
     function w_linkage(id_type)
     {
         var selected = $("#linkage_"+id_type+"_triger").find("option:selected").text();
         switch (selected)
         {
             case 'APA':
                 document.getElementById("linkage_"+id_type+"_echo").readOnly=false;
                 break;
             default :
             case 'AMS':
                 document.getElementById("linkage_"+id_type+"_echo").value="";
                 document.getElementById("linkage_"+id_type+"_echo").readOnly=true;
                 break;
         }
     }
 </script>

                <tr>
                    <td>位置分类： </td>
                    <td    >
                        <select class="form-control linkage_triger " name="page_position"  onclick="w_linkage('add')"  id="linkage_add_triger"  >
                            <option value="2" >APA</option>
                            <option value="1">AMS</option>
                        </select>
                    </td>
                </tr>
                <tr>
                    <td>keyword：</td>
                    <td><input type="text" name="keyword"></td>
                </tr>
                <tr>
                    <td>brand：</td>
                    <td><input type="text" name="brand"></td>
                </tr>
                <tr>
                    <td>adasin：</td>
                    <td><input type="text" name="adasin" placeholder="选AMS时，请跳过" id="linkage_add_echo"></td>
                </tr>

         <tr>
             <td>位置分类： </td>
             <td>
                 <select class="form-control" name="page_position_edit"  onclick="w_linkage('edit')"  id="linkage_edit_triger"  >
                     <option value="2" >APA</option>
                     <option value="1">AMS</option>
                 </select>
             </td>
         </tr>
         <tr>
             <td>keyword：</td>
             <td><input type="text" name="keyword_edit" value="<?= $_GET['keyword']?>"></td>
         </tr>
         <tr>
             <td>brand：</td>
             <td><input type="text" name="brand_edit" value="<?= $_GET['brand']?>"></td>
         </tr>
         <tr>
             <td>adasin：</td>
             <td><input type="text" name="adasin_edit"  placeholder="选AMS时，请跳过"  value="<?= $_GET['adasin']?>" id="linkage_edit_echo"></td>
         </tr>

//readyonly  交互，不绑架输入

// add edit  为同一脚本

问题：

 document.getElementById("linkage_"+id_type+"_echo").innerHTML="";
 document.getElementById("linkage_"+id_type+"_echo").innerText="";
 $("#linkage_"+id_type+"_echo").emprt();;

为什么失效？