<script>
var i = 1;
function add(val){
  var obj = document.getElementById("s").tBodies[0];
  var row = null;
  var cell = null;
  var input= null;
    row = document.createElement("tr");
    cell = document.createElement("td");
    input = document.createElement("input");
    input.setAttribute("type", "text");
    input.setAttribute("value", i.toString());
    cell.appendChild(input);
    row.appendChild(cell);

    cell = document.createElement("td");
    input = document.createElement("input");
    input.setAttribute("type", "button");
    input.setAttribute("value", "-");
    input.onclick=function(){del(this.parentNode.parentNode);};
    cell.appendChild(input);
    row.appendChild(cell);

    obj.appendChild(row);

    i+=1;
}

function del(obj){
  document.getElementById("s").tBodies[0].removeChild(obj);
}
</script>
<table id="s">
<thead>
<tr>
<td><input type="button" onclick="add()" value="+"/></td>
</tr>
</thead>
<tbody>
</tbody>
</table>