How to download a certain number of messages?

Question

PHP

Hello! I have a chat, messages are added to a text file and displayed on the site, how can I set a message output limit so that only 20 are displayed, for example?

<script>
load_messes();
setInterval(load_messes,2000);
function sendGo(e) {
if (e.keyCode == 13) {
$("#send_massage").click();
}
}
function toggleSmiles() {
  $(".smiles-box").fadeToggle('fast');
}
function smile(a) {
  $("#text-massage").val($("#text-massage").val() + " :" + a + ": ").focus();
  toggleSmiles();
}
</script>

<script>
    var scrolled;
    
    function load_messes()
    {
      $.ajax({
        type: "POST",
        url:  "chatread.php",
        data: "req=ok",
        success: function(test)
        {
        var $mcaht = $("#mcaht"),
          scroll = $mcaht.scrollTop(),
          messageCount = $mcaht.children().length;
    
        $mcaht.empty().append(test);
    
        scroll && $mcaht.scrollTop(scroll);
    
        if(!scrolled || messageCount < $mcaht.children().length) {
          $mcaht.scrollTop(9000000);
          !scrolled && (scrolled = true);
        }
    
        }
      });
    }
  </script>

Answer 1

this should be done in PHP

Answer 2

If you want to take EVERYTHING, and then decide on the client which of them to show, this is a gross mistake and an extra load on resources (the chat will start to slow down sooner or later).
The server logic must decide which list of messages to return for display.