var clone;
function cloneRow(){
var rows=document.getElementById('mytab').getElementsByTagName('tr');
var index=rows.length;
clone=rows[index-1].cloneNode(true);
var inputs=clone.getElementsByTagName('input'), inp, i=0 ;
while(inp=inputs[i++]){
inp.name=inp.name.replace(/\d/g,'')+(index+1);
}
}
function addRow(){
var tbo=document.getElementById('mytab').getElementsByTagName('tbody')[0];
tbo.appendChild(clone);
cloneRow();
}
onload=cloneRow;