JS控制表格隔行变色

<table width="800" border="0" cellpadding="0" cellspacing="0">
    <tr>
        <td>不变色</td>
    </tr>
    <tbody id="goaler">
    <tr>
        <td>xxxxxxxx</td>
    </tr>
    <tr>
        <td>xxxxxxxx</td>
    </tr>
    <tr>
        <td>xxxxxxxx</td>
    </tr>
    <tr>
        <td>xxxxxxxx</td>
    </tr>
    </tbody>
    <tr>
        <td>不变色</td>
    </tr>
</table>
<script language="javascript">
<!--
var tbrow = document.getelementbyid("goaler");
if (tbrow != null)
{
    for (var i=0;i<tbrow.rows.length ;i++ )
    {
        if (tbrow.rows[i].rowindex%2==1)
        {
            tbrow.rows[i].style.backgroundcolor="";
        }
        else
        {
            tbrow.rows[i].style.backgroundcolor="#f1f1f1";
        }
    }
}
//-->
</script>