在PHP中关闭模式后如何删除消息

如何解决在PHP中关闭模式后如何删除消息

我有一个小的示例代码，如果单击“登录”按钮，则在其中显示模式，如果在背景中的任意位置单击，则将关闭模式。

现在我要做的是删除关闭模态时的错误消息，以便当我通过单击登录按钮再次打开模态时，该消息被删除。但是，错误消息仍然存在。关闭模态时清除消息的最佳方法是什么？

 <?PHP
    
    $username_err = "";
    
    // Processing form data when form is submitted
    if($_SERVER["REQUEST_METHOD"] == "POST"){
     
     if ($_POST["Login"]){
    
    //The if statement below would handle incorrect user crednetial entry but not included in code
    if(...code to check if username is incorrect){
    $username_err = "Username Error";
    }
    
    }
    
    <div id="id01" class="modal">
     <span class="help-block"><?PHP echo $username_err; ?></span>
     <button type="submit" value="Login" name="Login">Enter</button>
    </div>

    
            <script>
            // Get the modal
            var modal = document.getElementById('id01');
            
            // When the user clicks anywhere outside of the modal,close it
            window.onclick = function(event) {
                if (event.target == modal) {
                    modal.style.display = "none";
                    <?PHP $username_err = ""; ?>
                }
            }
            
            </script>

没有运气尝试过

<?PHP if($_SERVER["REQUEST_METHOD"] == "POST"){
            if ($_POST["Login"]){
            echo "<script>
            document.getElementById('id01').style.display='block';
            document.getElementsByClassName('help-block').style.display='none';
}
            </script>";