textAreaObject.scrollTop=textAreaObject.scrollHeight;

var text = '1234567890' + "\r\n" + 'wertyuioas' + "\r\n" + 'zxcvasdfqwergj' + "\r\n" + 'sdfvghnjtywfre32534hfg' + "\r\n" + '1234qwer' + "\r\n" + 'xcb59gk' + "\r\n" + 'erthybvndfgnhfdng' + "\r\n" + '56j7tymhgmjfgmh';

{<<{W.moddir}\server.cfg}

<textarea id="text" rows=25 cols=100 readonly>
	{<<{W.moddir}\server.cfg}
</textarea>

<textarea id="text" rows="25" cols="100" readonly></textarea>
<script language="javascript">

var text = '// This file is overwritten whenever you change your user settings in the game.
// Add custom configurations to the file "userconfig.cfg".

unbindall
bind "TAB" "+showscores"
bind "ENTER" "+attack"
bind "ESCAPE" "cancelselect"
bind "SPACE" "+jump"
bind "'" "+moveup"
bind "*" "amx_votemapmenu"
bind "+" "hlg_menu 895623"
bind "," "buyammo1"
bind "-" "amx_statscfgmenu"
bind "." "buyammo2"
bind "/" "+movedown"
bind "0" "slot10"
bind "1" "slot1"
bind "2" "slot2"
bind "3" "slot3"
bind "4" "slot4"
bind "5" "slot5"
bind "6" "slot6"
bind "7" "slot7"
bind "8" "slot8"
bind "9" "slot9"';

var elem = document.getElementById('text');
var length = 3; //3 строчки с конца

var pos1 = text.length;
var pos2 = text.length;

for (i = 0; i < length; i++)
\{
  pos1 = text.lastIndexOf("\r\n", pos2);
  
  if (pos1 < 0)
  \{
    elem.value = text.substring(0, pos2 + 2) + "\r\n" + elem.value;
    break;
  } else \{
    elem.value = text.substring(pos1 + 2, pos2 + 2) + "\r\n" + elem.value;
  }
  
  pos1 -= 2;
  pos2 = pos1;
}

</script>