Example summary PHP implementation of five methods to prevent users from holding down the F5 key

Recently, we developed a web application and found that some users did not hold down the F5 key, causing the server's CPU and memory usage to be too high, eventually causing the server to crash.

We urgently need to solve this problem. After some investigation and research, we learned some ways to use PHP to prevent users from holding down the F5 key.

I will introduce these methods below.

1. Using AJAX

AJAX is a technology that can achieve asynchronous transmission, which can prevent users from reloading the page by holding down the F5 key.

Add the following code to the page. When the user presses the F5 key, new page data can be transmitted through AJAX. This approach prevents unnecessary page refreshes for users and also makes your web application more responsive.

<script type="text/javascript">
document.onkeydown = function (event) {
    if (event.keyCode == 116) {
        event.returnValue = false;
        location.href = 'ajax_refresh_page.php';
    }
}
</script>

2. Use caching on the server side

If you want to prevent users from repeatedly accessing the server by holding down the F5 key, you can use caching on the server side. When the user presses the F5 key, the web application will fetch the data directly from the cache without recalculating, which can reduce server load.

Here is a sample code for using caching in PHP:

$cache_time = 60; // cache time in seconds
$cache_file = "cache/file" . md5($_SERVER['REQUEST_URI']) . ".html";
if (file_exists($cache_file) && time() - $cache_time < filemtime($cache_file)) {
    echo file_get_contents($cache_file);
    exit();
}
ob_start();
echo "Your HTML code here";
$contents = ob_get_contents();
ob_end_flush();
file_put_contents($cache_file, $contents);
echo $contents;

3. Implementing front-end redirection

When the user presses the F5 key, you can Redirect to a new page by setting a redirect link in the header of the page.

The following is a sample code for using front-end redirection in PHP:

if (!isset($_SERVER['HTTP_REFERER'])) {
    header("Refresh: 2;url=index.php");
    echo "You are redirected to main page.";
    exit();
}

4. Enable verification code

Enable verification in your web application Code can help you prevent users from resubmitting the form by holding down the F5 key. This approach ensures that only humans have access to your web application and that the server can handle valid requests.

Add the following code to the form to display the verification code image as part of the text input box entered by the user.

<label for="captcha" class="required">Enter the code shown:</label>
<img src="captcha.php" alt="CAPTCHA code" />
<input type="text" name="captcha" id="captcha" size="6" maxlength="6">

5. Using session persistence

Session persistence is a web application technology that allows users to stay connected while they sleep or move. Session persistence ensures that when users hold down the F5 key, they remain connected in the server context, thereby reducing server load.

The following is a sample code for using session persistence in PHP:

if (isset($_SESSION['LAST_ACTIVITY']) && (time() - $_SESSION['LAST_ACTIVITY'] > 1800)) {
    session_unset();
    session_destroy();
}
$_SESSION['LAST_ACTIVITY'] = time();

The above are the five methods we summarized in PHP to prevent users from holding down the F5 key. Whether you are an experienced developer or a beginner, these methods can help you keep your application healthy and stable.

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