<script language="javascript">
function totopbottom()
{
    if (document.body.scrollHeight <= (document.body.clientHeight+document.body.scrollTop))
  {
        window.scrollTo(0,0);
    }
    else
    {
        window.scrollTo(0, document.body.scrollHeight);
    }
}
function topbottom()
{
    document.body.ondblclick = totopbottom;
}

topbottom();
</script>