Count Down Redirect Using JavaScript and PHP

countdown-redirect.php

<?php
/**
* These constants can be set elsewhere in your project, ideally in a configuration file. 
*/
if ( ! defined( 'COUNTDOWN_REDIRECT_LOCATION' ) ) {
	define('COUNTDOWN_REDIRECT_LOCATION', 'https://google.com');
}
if ( ! defined( 'COUNTDOWN_REDIRECT_SECONDS' ) ) {
	define('COUNTDOWN_REDIRECT_SECONDS', 15);
}
?>
<!-- Modify this according to your requirement -->
<h3>
    Redirecting to <a href="<?=COUNTDOWN_REDIRECT_DESTINATION;?>"><?=COUNTDOWN_REDIRECT_DESTINATION;?></a> after <span id="countdown"><?=COUNTDOWN_REDIRECT_SECONDS;?></span> seconds.
</h3>

<!-- JavaScript part -->
<script type="text/javascript">
    
    // Total seconds to wait
    var seconds = <?=COUNTDOWN_REDIRECT_SECONDS;?>;
    var destination = "<?=COUNTDOWN_REDIRECT_DESTINATION;?>"; 
    
    function countdown() {
        seconds = seconds - 1;
        if (seconds < 0) {
            // Chnage your redirection link here
            window.location = destination;
        } else {
            // Update remaining seconds
            document.getElementById("countdown").innerHTML = seconds;
            // Count down using javascript
            window.setTimeout("countdown()", 1000);
        }
    }
    
    // Run countdown function
    countdown();
    
</script>