[急]如何删除所有的Table子节点(tr,td)

<html>
<head>
<title></title>
<script language="JavaScript">
window.onload = function()
{
    T();
}function T()
{
    var t = document.getElementById("tab");
    if(t.rows.length > 0)
    {
        t.deleteRow(0);
        setTimeout("T()", 1000);
    }    
}
</script>
</head>
<body>
<TABLE id="tab" border="1">
<TR><TD>1</TD><TD>2</TD><TD>3</TD><TD>4</TD></TR>
<TR><TD>5</TD><TD>6</TD><TD>7</TD><TD>8</TD></TR>
<TR><TD>9</TD><TD>10</TD><TD>11</TD><TD>12</TD></TR>
<TR><TD>13</TD><TD>14</TD><TD>15</TD><TD>16</TD></TR>
</TABLE></body>
</html>