var i, temp,
frag = document.createDocumentFragment(),
li   = document.createElement('li');
for ( i=0; i<3; i++ )
{
  temp = li.cloneNode( true );
  temp.appendChild(
    document.createTextNode(
      'This is new list item number ' + ( i + 1 )
    )
  );
  frag.appendChild( temp );
}
document.getElementById('the-list').appendChild( frag );