user menu chat

$('#list_user').on('click','.click-list-chat',function(){
        var user_ID = $(this).attr('id');
        var last_ID = "0";
        $.ajax({
            type: "POST",
            global: false,
            url: "<?=BASE_ACTION?>/chat/isi/?kepada_user_ID="+user_ID,
            success: function(html) {
                    $('#isi_chat').html(html);
                    $('#kepada_user_ID').val(user_ID);
                    var scroll = $('ul .collection');
                    var height = scroll[0].scrollHeight;
                    scroll.scrollTop(height);
                    $.ajax({
                        type: "POST",
                        global: false,
                        url: "<?=BASE_ACTION?>/chat/checking_last_history_chat/?kepada_user_ID="+user_ID,
                        success: function(html) {
                            last_ID = html;
                            setInterval(function(){

                                $.ajax({

                                    type: "POST",
                                    global: false,
                                    url: "<?=BASE_ACTION?>/chat/checking_last_history_chat/?kepada_user_ID="+user_ID,
                                    success: function(html) {
                                        if(html != last_ID) {
                                            last_ID = html;
                                            $.ajax({
                                                type: "POST",
                                                global: false,
                                                url: "<?=BASE_ACTION?>/chat/isi/?kepada_user_ID="+user_ID,
                                                success: function(html) {
                                                    $('#isi_chat').html(html);
                                                    $('#kepada_user_ID').val(user_ID);
                                                    var scroll = $('ul .collection');
                                                    var height = scroll[0].scrollHeight;
                                                    scroll.scrollTop(height);
                                                }
                                            });
                                        }
                                    }

                                });

                            },2000);
                        }
                    });
            }
        });


    });