my custom modifications to the chat

My JS:
======
    // jQuery Document
    $(document).ready(function(){
        //If user wants to end session
        $("#exit").click(function() {
            var exit = confirm("Are you sure you want to end the session?");
            if(exit==true){window.location = 'index.php?logout=true';}
        });

        //If user submits the form
        $("#submitmsg").click(function() {
            var clientmsg = $("#usermsg").val();
            $.post("post.php", {text: clientmsg});
            $("#usermsg").attr("value", "");
            return false;
        });

        //Load the file containing the chat log
        function loadLog(){
            var oldscrollHeight = $("#chatbox").attr("scrollHeight") - 20; //Scroll height before the request
            $.ajax({
                url: "log.php",
                cache: false,
                success: function(html) {
                    $("#chatbox").html(html); //Insert chat log into the #chatbox div

                    //Auto-scroll
                    var newscrollHeight = $("#chatbox").attr("scrollHeight") - 20; //Scroll height after the request
                    if(newscrollHeight > oldscrollHeight){
                        $("#chatbox").animate({ scrollTop: newscrollHeight }, 'normal'); //Autoscroll to bottom of div
                    }
/**
 * Here, the change starts!!!
/**/
                },
                complete: function() {
                     setTimeout(loadLog, 500);
                }
            });
        }
        loadLog();
    });

/**
 * End of Javascript
/**/


I created log.php, too.

log.php:
========
<?php
while((!file_exists("log.html") || filemtime("log.html") < (time()-4) ) && time()%20) { //Don't change the 20 to a high number. Leave some space to 30. To high numbers can cause Network-Timeout-Errors
    sleep(1);
    clearstatcache(true,"log.html");
}

echo file_get_contents("log.html");
?>