它们保留在字段中，因为您明确告诉 PHP 用提交的数据填写表单。

<input name="firstname" type="text" placeholder="First Name" required="required" 
value="<?php echo $_POST['firstname'];?>">
       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ HERE

只需删除它，或者如果您希望条件不这样做，请对该echo进行if语句，或者只是清理$_POST字段。

$_POST = array(); // lets pretend nothing was posted

或者，如果成功，将用户重定向到另一个页面：

header("Location: success.html");
exit; // Location header is set, pointless to send HTML, stop the script

顺便说一下，这是首选方法。如果将用户保留在通过POST方法访问的页面中，则如果他刷新页面，将再次提交表单。

表单上使用.reset()。

$(".myform")[0].reset();

我遇到了类似的问题，不想使用 header(( 重定向到另一个页面。

溶液：

使用 $_POST = array(); 重置窗体顶部的 $_POST 数组以及用于处理窗体的代码。

错误或成功消息可以有条件地添加到表单之后。希望这对:)有所帮助

这是当 for 与成功消息一起提交时要清除的所有表单字段的解决方案。 为此，设置值等于 false 检查下面的代码

<?php
$result_success = '';
$result_error = '';
$full_Name_error = $email_error = $msg_error = '';
$full_Name = $email = $msg = $phoneNumber = '';
$full_Name_test = $email_test = $msg_test = '';
//when the form is submitted POST Method and must be clicked on submit button
if ($_SERVER['REQUEST_METHOD'] == "POST" && isset($_POST['form-submit'])) {
    $full_Name = $_POST['fullName'];
    $email = $_POST['email'];
    $phoneNumber = $_POST['phoneNumber'];
    $msg = $_POST['message'];
    // Form Validation for fullname
    if (empty($full_Name)) {
        $full_Name_error = "Name is required";
    } else {
        $full_Name_test = test_input($full_Name);
        if (!preg_match("/^[a-z A-Z]*$/", $full_Name_test)) {
            $full_Name_error = "Only letters and white spaces are allowed";
        }
    }
    //Form Validation for email
    if (empty($email)) {
        $email_error = "Email is required";
    } else {
        $email_test = test_input($email);
        if (!filter_var($email_test, FILTER_VALIDATE_EMAIL)) {
            $email_error = "Invalid Email format";
        }
    }
    //Form Validation for message
    if (empty($msg)) {
        $msg_error = "Say atleast Hello!";
    } else {
        $msg_test = test_input($msg);
    }
    if ($full_Name_error == '' and $email_error == '' and $msg_error == '') {
        // Here starts PHP Mailer 
        date_default_timezone_set('Etc/UTC');
        // Edit this path if PHPMailer is in a different location.
        require './PHPMailer/PHPMailerAutoload.php';
        $mail = new PHPMailer;
        $mail->isSMTP();
        /*Server Configuration*/
        $mail->Host = 'smtp.gmail.com'; // Which SMTP server to use.
        $mail->Port = 587; // Which port to use, 587 is the default port for TLS security.
        $mail->SMTPSecure = 'tls'; // Which security method to use. TLS is most secure.
        $mail->SMTPAuth = true; // Whether you need to login. This is almost always required.
        $mail->Username = ""; // Your Gmail address.
        $mail->Password = ""; // Your Gmail login password or App Specific Password.
        /*Message Configuration*/
        $mail->setFrom($email, $full_Name); // Set the sender of the message.
        $mail->addAddress(''); // Set the recipient of the message.
        $mail->Subject = 'Contact form submission from your Website'; // The subject of the message
        /*Message Content - Choose simple text or HTML email*/
        $mail->isHTML(true);
        // Choose to send either a simple text email...
        $mail->Body = 'Name: ' . $full_Name . '<br>' . 'PhoneNumber:  ' . $phoneNumber . '<br>' . 'Email:  ' . $email . '<br><br>' . 'Message:  ' . '<h4>' . $msg . '</h4>'; // Set a plain text body.
        // ... or send an email with HTML.
        //$mail->msgHTML(file_get_contents('contents.html'));
        // Optional when using HTML: Set an alternative plain text message for email clients who prefer that.
        //$mail->AltBody = 'This is a plain-text message body'; 
        // Optional: attach a file
        //$mail->addAttachment('images/phpmailer_mini.png');
        if ($mail->send()) {
            $result_success = "Your message was sent successfully!  " . 
            //Here is the solution for when the for is submitted with the successful message all form fields to get cleared.
            $full_Name;
            $full_Name = false;
            $email = false;
            $phoneNumber = false;
            $msg = false;
        } else {
            $result_error = "Something went wrong. Check your Network connection and Please try again.";
        }
    }
}
function test_input($data)
{
    $data = trim($data);
    $data = stripslashes($data);
    $data = htmlspecialchars($data);
    return $data;
}

保存提交的表单数据的 POST 数据在表单中回显，例如：

<input name="firstname" type="text" placeholder="First Name" required="required" 
value="<?php echo $_POST['firstname'];?>"  

表单后清除 POST 数据 - 即所有输入都正常，并且您已经对表单的结果采取了任何操作。
或者，一旦您确定表单正常并执行了表单中的任何操作，请将用户重定向到新页面以说"全部完成，谢谢"等。

header('Location: thanks.php');
exit();

这会阻止 POST 数据存在，它被称为"发布/重定向/获取"：
http://en.wikipedia.org/wiki/Post/Redirect/Get

发布/重定向/获取 (PRG( 方法和使用另一个页面还可以确保如果用户单击浏览器刷新或后退按钮导航到其他位置，则不会再次提交表单。
这意味着如果您的表单插入数据库或向某人发送电子邮件(等(，如果没有 PRG 方法，则每次他们单击刷新或使用历史记录/后退按钮重新访问页面时，都会(可能(插入/通过电子邮件发送值。

将onClick函数放在按钮提交中：

<input type="text" id="firstname">
<input type="text" id="lastname">
<input type="submit" value="Submit" onClick="clearform();" />

在<head>中，定义函数 clearform((，并将文本框值设置为 "" ：

function clearform()
{
    document.getElementById("firstname").value=""; //don't forget to set the textbox id
    document.getElementById("lastname").value="";
}

这样，当您单击提交按钮时，文本框将被清除。

我只是想修复同样的错误，我终于修复了它，所以我会复制部分代码给你，也许它对你有帮助。

<input type="text" name="usu" id="usu" value="<?php echo $usu;?>" ></input>
<input type="text" name="pass" id="pass" value="<?php echo $varpass;?>"></input>  

这些是我按下按钮后想要清理的输入。

这里是 php 代码：

$query= "INSERT INTO usuarios (tipo, usuario, password) VALUES ('".$vartipo."', '".$usu."', '".$varpass."')";

        if (!mysqli_query($conexion,$query)){
            die('Error: ' . mysqli_error($conexion));
        }
        else{

            $usu = '';  
            $varpass= '';   
            $result = '<div class="result_ok">El usuario se ha registrado con éxito! <div>';        

        }

$usu = '';
$varpass= '';

这些是清理输入:D的行

这段代码会帮助你

if($insert){$_POST['name']="";$_POST['content']=""}

如果您希望清除表单的字段，则只需在 onClick 事件中添加延迟，如下所示：

<input name="submit" id="MyButton" type="submit" class="btn-lg" value="ClickMe" onClick="setTimeout('clearform()', 2000 );"
onClick="setTimeout('clearform()', 1500 );" . in 1,5 seconds its clear
document.getElementById("name").value = "";  <<<<<<just correct this
document.getElementById("telephone").value = "";    <<<<<correct this

clearform()，我的意思是你的清理场功能。

// This file is PHP.
<html>    
<?php
    if ($_POST['submit']) {
        $firstname = $_POST['firstname'];
        $lastname = $_POST['lastname'];
        $email = $_POST['email'];
        $password = $_POST['password'];
        $confirmpassword = $_POST['confirmpassword'];
        $strtadd1 = $_POST['strtadd1'];
        $strtadd2 = $_POST['strtadd2'];
        $city = $_POST['city'];
        $country = $_POST['country'];
        $success = '';

        // Upon Success.
        if ($firstname != '' && $lastname != '' && $email != '' && $password != '' && $confirmpassword != '' && $strtadd1 != '' && $strtadd2 != '' && $city != '' && $country != '') {
            // Change $success variable from an empty string.
            $success = 'success';
            // Insert whatever you want to do upon success.
        } else {
            // Upon Failure.
            echo '<p class="error">Fill in all fields.</p>';
            // Set $success variable to an empty string.
            $success = '';
        }
    }
   ?>
<form method="POST" action="#">
    <label class="w">Plan :</label>
    <select autofocus="" name="plan" required="required">
        <option value="">Select One</option>
        <option value="FREE Account">FREE Account</option>
        <option value="Premium Account Monthly">Premium Account Monthly</option>
        <option value="Premium Account Yearly">Premium Account Yearly</option>
    </select>
    <br>
    <label class="w">First Name :</label><input name="firstname" type="text" placeholder="First Name" required="required" value="<?php if (isset($firstname) && $success == '') {echo $firstname;} ?>"><br>
    <label class="w">Last Name :</label><input name="lastname" type="text" placeholder="Last Name" required="required" value="<?php if (isset($lastname) && $success == '') {echo $lastname;} ?>"><br>
    <label class="w">E-mail ID :</label><input name="email" type="email"  placeholder="Enter Email" required="required" value="<?php if (isset($email) && $success == '') {echo $email;} ?>"><br>
    <label class="w">Password :</label><input name="password" type="password" placeholder="********" required="required" value="<?php if (isset($password) && $success == '') {echo $password;} ?>"><br>
    <label class="w">Re-Enter Password :</label><input name="confirmpassword" type="password" placeholder="********" required="required" value="<?php if (isset($confirmpassword) && $success == '') {echo $confirmpassword;} ?>"><br>
    <label class="w">Street Address 1 :</label><input name="strtadd1" type="text" placeholder="street address first" required="required" value="<?php if (isset($strtadd1) && $success == '') {echo $strtadd1;} ?>"><br>
    <label class="w">Street Address 2 :</label><input name="strtadd2" type="text" placeholder="street address second"  value="<?php if (isset($strtadd2) && $success == '') {echo $strtadd2;} ?>"><br>
    <label class="w">City :</label><input name="city" type="text" placeholder="City" required="required" value="<?php if (isset($city) && $success == '') {echo $city;} ?>"><br>
    <label class="w">Country :</label><select autofocus="" id="a1_txtBox1" name="country" required="required" placeholder="select one" value="<?php if (isset($country) && $success == '') {echo $country;} ?>">
    <input type="submit" name="submit">
</form>
</html>

使用value="<?php if (isset($firstname) && $success == '') {echo $firstname;} ?>"
然后，您必须创建$success变量 - 就像我在示例中所做的那样。