DOM remove TABLE tr

function change()
		{											   
			//alert(document.getElementById("tab").childNodes.length);   length=1
			//alert(document.getElementById("tab").lastChild.nodeName);	 nodeName=TBODY
			for(var i=0; i < document.getElementById("tab").childNodes.length;i++)
			 {
			 	var Ttable = document.getElementById("tab").childNodes[i];
			 	//alert(Ttable.firstChild.nodeName); tr
			 	//alert(Ttable.childNodes.length);  3
			 	for(var j=0;j<Ttable.childNodes.length;j++)
			 	{
			 		var tr = Ttable.childNodes[j+1];
			 		if(tr!=null)
			 		{
			 			Ttable.removeChild(tr);
			 		}
			 	}
			 }

			//alert(document.getElementById("tr1").firstChild.nodeName); nodeName= TD
			//alert(document.getElementById("tr1").childNodes.length);   length = 2
			for(var i=0;i<document.getElementById("tr1").childNodes.length;i++)
			{
				var tr = (document.getElementById("tr1").childNodes)[i];
				document.getElementById("tr1").removeChild(tr);
			}
		}

<table align="center" border="2" bgcolor="#9fdfd1" id="tab">
 		<tr> 
 			<td align="center" colspan="2"><input type="button" value="OK" onClick="change();"/></td>
 		</tr>
 		<tr>
 			<td>AAA</td>
 			<td>BBB</td>
 		</tr>
 		<tr id="tr1">
 			<td>AAA</td>
 			<td>BBB</td>
 		</tr>
 	</table>