How to Implement Debounce and Prevent Duplicate Submissions in PHP

Debounce Function Implementation

Debounce ensures that a specific operation runs only once within a defined time window. In PHP, the session can store a timer to achieve this.

Create a file named debounce.php with the following content:

<?php
session_start();

function debounce($callback, $delay = 1000) {
    if (isset($_SESSION['debounce_timer'])) {
        return;
    }
    $callback();
    $_SESSION['debounce_timer'] = time() + $delay;
    register_shutdown_function('debounce_reset_timer');
}

function debounce_reset_timer() {
    unset($_SESSION['debounce_timer']);
}

Use the debounce() function to wrap any event, such as an AJAX request triggered by user input:

<?php
function handleInput() {
    // Process AJAX request
}

debounce('handleInput', 1000);

Here, handleInput() is the function that processes the request, and 1000 represents a 1‑second debounce delay. Rapid consecutive inputs will result in only the final call being executed.

Anti‑Duplicate Submission Implementation

To prevent users from submitting the same form repeatedly, generate a unique token stored in the session and embed it as a hidden field in the form.

<?php
session_start();

function generateToken() {
    $_SESSION['submit_token'] = md5(uniqid(rand(), true));
    return $_SESSION['submit_token'];
}

$token = generateToken();

Insert the token into the form as a hidden input:

<input type="hidden" name="submit_token" value="<?php echo $token; ?>">

When processing the form, validate the submitted token against the one stored in the session:

<?php
session_start();

function validateToken($token) {
    if (isset($_SESSION['submit_token']) && $token === $_SESSION['submit_token']) {
        unset($_SESSION['submit_token']);
        return true;
    }
    return false;
}

if ($_POST && validateToken($_POST['submit_token'])) {
    // Handle form submission logic
}

If the tokens match, the form is processed; otherwise, the request is identified as a duplicate submission and can be handled accordingly (e.g., display a warning to the user).

By combining session storage with a debounce timer and a token‑based verification, PHP developers can effectively control rapid event firing and prevent duplicate form submissions.