filename-based-cache-busting.php

<?php
/**
 * Filename-based cache busting for WordPress scripts/styles.
 *
 * Extend your .htaccess file with these lines:
 *
 *   <IfModule mod_rewrite.c>
 *     RewriteEngine On
 *     RewriteBase /
 *
 *     RewriteCond %{REQUEST_FILENAME} !-f
 *     RewriteCond %{REQUEST_FILENAME} !-d
 *     RewriteRule ^(.+)\.(.+)\.(js|css)$ $1.$3 [L]
 *   </IfModule>
 *
 * @param  string $src The source with ?ver= suffix
 * @return string e.g http://host.com/style.FILE_TIMESTAMP.css
 */
function filename_based_cache_busting($src) {
  
	// Don't touch admin scripts.
	if (is_admin()) {
		return $src;
	}

	// Remove version string from the source.
	$src = preg_replace('/\?ver=(.+)/', '', $src);
	
	// Only for scripts on current domain
	$domain = $_SERVER['HTTP_HOST'];
	if (strpos($src, $domain) == false) {
		return $src;
	}

	// Get the sources local file path
	$src_local_path = str_replace(get_site_url(), ABSPATH, $src);

	// Get the files last updated timestamp
	$timestamp = filemtime($src_local_path);

	// Get the extension of the file, can be '.js' or '.css'.
	$ext = '.' . pathinfo($src, PATHINFO_EXTENSION);

	// Build the new source.
	$src = str_replace($ext, '.' . $timestamp . $ext, $src);

	// Return the new source.
	return $src;

}

add_filter('script_loader_src', 'filename_based_cache_busting');
add_filter('style_loader_src', 'filename_based_cache_busting');