怎样获取鼠标所在表的行号?

Question

<table border="1" cellspacing="0" cellpadding="0" width="100%" id="tb">
  <tr onclick="foo(this)">       
    <td valign="top" align="left" id="mytds">a</td>
    <td align="left" valign="top" id ="mylist">a</td> 
  </tr>
  <tr onclick="foo(this)">       
    <td valign="top" align="left" id="mytds">a</td>
    <td align="left" valign="top" id ="mylist">a</td> 
  </tr>
  <tr onclick="foo(this)">       
    <td valign="top" align="left" id="mytds">a</td>
    <td align="left" valign="top" id ="mylist">a</td> 
  </tr>
  <tr onclick="foo(this)">       
    <td valign="top" align="left" id="mytds">a</td>
    <td align="left" valign="top" id ="mylist">a</td> 
  </tr>
</table>   
</body>
<script type="text/javascript">
//<![CDATA[
function foo(o){
var a=document.getElementById("tb").getElementsByTagName("TR");
for (var i=0; i<a.length; i++){
a[i]==o?alert(a[i].rowIndex):""
}
}
//]]>
</script>

Answer 1

<TABLE width="60%" border="1">
    <TR onmousemove="showLineNumber(this.rowIndex)" >
      <TD>Line 0</TD>
    </TR>
    <TR onmousemove="showLineNumber(this.rowIndex)">
      <TD>Line 1</TD>
    </TR>
    <TR onmousemove="showLineNumber(this.rowIndex)">
      <TD>Line 2</TD>
    </TR>
</TABLE>
<div id="LineNumber"></div>
<SCRIPT LANGUAGE="JavaScript">
<!--
function showLineNumber(rowIndex){
    LineNumber.innerHTML = "Line number:&nbsp;" + rowIndex;
}
//-->
</SCRIPT>

Answer 2

看来是我写代码写晕了，我上面的原意这样<table border="1" cellspacing="0" cellpadding="0" width="100%" id="tb">
  <tr>       
    <td valign="top" align="left" id="mytds">a</td>
    <td align="left" valign="top" id ="mylist">a</td> 
  </tr>
  <tr>       
    <td valign="top" align="left" id="mytds">a</td>
    <td align="left" valign="top" id ="mylist">a</td> 
  </tr>
  <tr>       
    <td valign="top" align="left" id="mytds">a</td>
    <td align="left" valign="top" id ="mylist">a</td> 
  </tr>
  <tr>       
    <td valign="top" align="left" id="mytds">a</td>
    <td align="left" valign="top" id ="mylist">a</td> 
  </tr>
</table>   
</body>
<script type="text/javascript">
//<![CDATA[
onload = function(){
var a=document.getElementById("tb").getElementsByTagName("TR");
for (var i=0; i<a.length; i++){
a[i].onclick=function(){alert(this.rowIndex)};
}
}
//]]>
</script>