html通过draggable如何实现将拖放后位置原有的内容删除？

模拟车在车库中换车位的过程，将车从一个车位拖到其余的空车位上，然后让空车位原有的图片消失，显示拖动的车的图片。目前只实现了一部分，如下：
代码如下：

    <script>
        function allowDrop(ev)
        {
            ev.preventDefault();
        }
        function drag(ev)
        {
            ev.dataTransfer.setData("Text",ev.target.id);
        }
        function drop(ev)
        {
            ev.preventDefault();
            var data=ev.dataTransfer.getData("Text");
            ev.target.appendChild(document.getElementById(data));
        }
    </script>
    <style>
        #tal1 td{
            border: 1px solid black;
        }
    </style>
    <table width="300px" height="300px">
        <tr>
            <td ondrop="drop(event)" ondragover="allowDrop(event)"><img draggable="true" ondragstart="drag(event)" id="im1" src="img/1.png"/></td>
            <td ondrop="drop(event)" ondragover="allowDrop(event)"><img draggable="true" ondragstart="drag(event)" id="im2" src="img/1.png"/></td>
            <td ondrop="drop(event)" ondragover="allowDrop(event)"><img id="im3" src="img/e.png"/></td>
        </tr>
        <tr>
            <td ondrop="drop(event)" ondragover="allowDrop(event)"><img draggable="true" ondragstart="drag(event)" id="im4" src="img/1.png"/></td>
            <td ondrop="drop(event)" ondragover="allowDrop(event)"><img id="im5" src="img/e.png"/></td>
            <td ondrop="drop(event)" ondragover="allowDrop(event)"><img id="im6" src="img/e.png"/></td>
        </tr>
        <tr>
            <td ondrop="drop(event)" ondragover="allowDrop(event)"><img id="im7" src="img/e.png"/></td>
            <td ondrop="drop(event)" ondragover="allowDrop(event)"><img id="im8" src="img/e.png"/></td>
            <td ondrop="drop(event)" ondragover="allowDrop(event)"><img id="im9" src="img/e.png"/></td>
        </tr>
    </table>

  <script>
        function allowDrop(ev)
        {
            ev.preventDefault();
        }
        function drag(ev)
        {   var oid = ev.target.id
            if(!oid){
                oid = "dragging" + (Date.now()+ Math.floor(Math.random()*1000 + 100)); //生成随机的 id
                ev.target.setAttribute("id",oid);
            }
            ev.dataTransfer.setData("Text",oid);
        }
        function drop(ev)
        {
            ev.preventDefault();
            var data=ev.dataTransfer.getData("Text");
            var dom = document.getElementById(data);
            var parent = dom.parentNode;
            parent.className = ""; //把 drop 类名去掉,显示出空位

            ev.target.className = "empty"; //加上 drop 类名,隐藏空位
            ev.target.appendChild(dom);
        }
    </script>
    <style>
        #tal1 td{
            border: 1px solid black;
        }
         #tal1 td.drop .empty{
             display: none;
         }
    </style>
    <table width="300px" height="300px">
        <tr>
            <td ondrop="drop(event)" ondragover="allowDrop(event)" class="drop">
                <img draggable="true" ondragstart="drag(event)"    src="img/1.png"/>
                <img  src="img/e.png" class="empty" />
            </td>
           <td ondrop="drop(event)" ondragover="allowDrop(event)">
            <img draggable="true" ondragstart="drag(event)"    src="img/1.png"/>
            <img  src="img/e.png" class="empty" />
           </td>
            <td ondrop="drop(event)" ondragover="allowDrop(event)">
                <img  src="img/e.png" class="empty" />
            </td>
        </tr>
        <tr>
            <td ondrop="drop(event)" ondragover="allowDrop(event)">
                <img  src="img/e.png" class="empty" />
            </td>
           <td ondrop="drop(event)" ondragover="allowDrop(event)">
            <img  src="img/e.png" class="empty" />
           </td>
            <td ondrop="drop(event)" ondragover="allowDrop(event)">
                <img  src="img/e.png" class="empty" />
            </td>
        </tr>
      <tr>
          <td ondrop="drop(event)" ondragover="allowDrop(event)">
            <img  src="img/e.png" class="empty" />
        </td>
         <td ondrop="drop(event)" ondragover="allowDrop(event)">
            <img  src="img/e.png" class="empty" />
         </td>
          <td ondrop="drop(event)" ondragover="allowDrop(event)" class="drop">
            <img draggable="true" ondragstart="drag(event)"   src="img/1.png"/>
            <img  src="img/e.png" class="empty" />
          </td>
      </tr>
    </table>

大概就是这样了