提交后无法刷新页面

我正在尝试让我的页面在提交时刷新，但它不会。

这是代码

PHP页面...

<?php
            if ($_SERVER['REQUEST_METHOD'] == 'POST')
            {
                //check if its an ajax request, exit if not
                if(!isset($_SERVER['HTTP_X_REQUESTED_WITH']) AND strtolower($_SERVER['HTTP_X_REQUESTED_WITH']) != 'xmlhttprequest') {
                } 
                //check $_POST vars are set, exit if any missing
                if(!isset($_POST["username"]) || !isset($_POST["message"]))
                {
                    $output = json_encode(array('type'=>'error', 'text' => 'Input fields are empty!'));
                    die($output);
                }
                //Sanitize input data using PHP filter_var().
                $username       = filter_var(trim($_POST["username"]), FILTER_SANITIZE_STRING);
                $message        = filter_var(trim($_POST["message"]), FILTER_SANITIZE_STRING);
                //additional php validation
                if(strlen($username)<4) // If length is less than 4 it will throw an HTTP error.
                {
                    $output = json_encode(array('type'=>'error', 'text' => 'Name is too short!'));
                    die($output);
                }
                if(strlen($message)<5) //check emtpy message
                {
                    $output = json_encode(array('type'=>'error', 'text' => 'Too short message!'));
                    die($output);
                }
                require('config.php');
                $sql="INSERT INTO guestbook(name, comment, datetime) VALUES('$username','$message', now())";
                header("Location:thanks.php");

            }
            ?>      

这是JS页面

$(document).ready(function(){
                $("#submit").click(function() { 
                    //get input field values
                    var name            = $('#name').val(); 
                    var message         = $('#comment').val();
                    var flag = true;
                    /********validate all our form fields***********/
                    if(name==""){ 
                        $('#name').css('border-color','red'); 
                        flag = false;
                    }
                    if(message=="") {  
                       $('#comment').css('border-color','red'); 
                        flag = false;
                    }
                    /********Validation end here ****/
                    /* If all are ok then we send ajax request to email_send.php *******/
                    if(flag) 
                    {
                        $.ajax({
                            type: 'post',
                            url: "thanks.php", 
                            dataType: 'json',
                            data: 'username='+name+'&message='+message,
                            beforeSend: function() {
                                $('#submit').attr('disabled', true);
                                $('#submit').after('<span class="wait">&nbsp;<img src="image/loading.gif" alt="" /></span>');
                            },
                            complete: function() {
                                $('#submit').attr('disabled', false);
                                $('.wait').remove();
                            },  
                            success: function(data)
                            {
                                if(data.type == 'error')
                                {
                                    output = '<div class="error">'+data.text+'</div>';
                                }else{
                                    output = '<div class="success">'+data.text+'</div>';
                                    $('input[type=text]').val(''); 
                                    $('#guestform textarea').val(''); 
                                }
                                $("#result").hide().html(output).slideDown();           
                                }
                        });
                    }
                });
                //reset previously set border colors and hide all message on .keyup()
                $("#guestform input, #guestform textarea").keyup(function() { 
                    $("#guestform input, #guestform textarea").css('border-color',''); 
                    $("#result").slideUp();
                });
            });

我将标题信息放在 PHP 中，但每次我点击提交时，它都会将数据保存在数据库中，然后只停留在页面上......文本区域中的文本也保留在那里。我希望它刷新页面，使其再次看起来像空白表单。