<form action="#">
<p>
<input type="button" value="最下行に1行挿入" onclick="fTalbeInsertRow()">
<input type="button" value="最下行から1行削除" onclick="fTalbeDeleteRow()">
</p>
</form>
<div class="tbl">
<table id="tableJ">
<tr><th>item1</th><td>1-1</td><td>1-2</td><td>1-3</td></tr>
<tr><th>item2</th><td>2-1</td><td>2-2</td><td>2-3</td></tr>
<tr><th>item3</th><td>3-1</td><td>3-2</td><td>3-3</td></tr>
</table>
</div>
<script>
function fTalbeDeleteRow(){
var tObj=document.getElementById("tableJ");
/* 行数 */
var idx=tObj.rows["length"];
if(idx<1) return false;
/* 1行挿入(最終行から削除)*/
tObj.deleteRow(idx-1);
}
function fTalbeInsertRow(){
var tObj=document.getElementById("tableJ");
/* 行数 */
var idx=tObj.rows["length"];
var idy=idx+1;
/* 1行挿入(最終行に挿入)*/
var insObj=tObj.insertRow(idx);
//var n=insObj.insertCell(0);
var n=document.createElement("th"); insObj.appendChild(n);
var x=insObj.insertCell(1)
var y=insObj.insertCell(2)
var z=insObj.insertCell(3)
n.innerHTML="item"+idy;
x.innerHTML=idy+"-1";
y.innerHTML=idy+"-2";
z.innerHTML=idy+"-3";
}
</script>