How can differences between browser cache and server-side code versions impact the functionality of PHP scripts, and how can this be resolved?

When there are differences between browser cache and server-side code versions, it can lead to inconsistencies in the functionality of PHP scripts. To resolve this issue, you can add versioning to your static assets like CSS, JavaScript, and images. By appending a version number or timestamp to the URL of these assets, you can ensure that the browser fetches the latest version whenever changes are made to the code.

<link rel="stylesheet" type="text/css" href="styles.css?v=<?php echo filemtime('styles.css'); ?>">
<script src="script.js?v=<?php echo filemtime('script.js'); ?>"></script>