如何知道某个表格中有多少行？即有多少tr

Question

alert(document.getElementById("tableid").childNodes[0].childNodes.length)

Answer 1

alert( document.all.theTable.rows.length )

Answer 2

<table id="abc">
<tr>
<td>1</td><td>11</td>
</tr>
<tr>
<td>2</td><td>22</td>
</tr>
<tr>
<td>3</td><td>33</td>
</tr>
<tr>
<td>4</td><td>444</td>
</tr>
</table>
<input type="button" value="行数" onClick="alert(abc.children[0].children.length)">