Automatic CSS/JavaScript Cache Busting

    /**

	 * Replace the `ver` query arg with the file's last modified timestamp

	 *

	 * @param  string $src URL to a file

	 * @return string      Modified URL to a file

	 */

	function filter_cache_busting_file_src( $src = '' ) {

		global $wp_scripts;

		// If $wp_scripts hasn't been initialized then bail.

		if ( ! $wp_scripts instanceof WP_Scripts ) {

			return $src;

		}

		// Check if script lives on this domain. Can't rewrite external scripts, they won't work.

		$base_url = apply_filters( 'rh/cache_busting_path/base_url', $wp_scripts->base_url, $src );

		if ( ! strstr( $src, $base_url ) ) {

			return $src;

		}

		// Remove the 'ver' query var: ?ver=0.1

		$src   = remove_query_arg( 'ver', $src );

		$regex = '/' . preg_quote( $base_url, '/' ) . '/';

		$path  = preg_replace( $regex, '', $src );

		// If the folder starts with wp- then we can figure out where it lives on the filesystem

		$file = null;

		if ( strstr( $path, '/wp-' ) ) {

			$file = untrailingslashit( ABSPATH ) . $path;

		}

		if ( ! file_exists( $file ) ) {

			return $src;

		}

		$time_format     = apply_filters( 'rh/cache_busting_path/time_format', 'Y-m-d_G-i' );

		$modified_time   = filemtime( $file );

		$timezone_string = get_option( 'timezone_string' );

		if ( empty( $timezone_string ) ) {

			$timezone_string = 'Etc/GMT';

		}

		$dt = new DateTime( '@' . $modified_time );

		$dt->setTimeZone( new DateTimeZone( $timezone_string ) );

		$time = $dt->format( $time_format );

		$src  = add_query_arg( 'ver', $time, $src );

		return $src;

	}

add_filter( 'script_loader_src', 'filter_cache_busting_file_src' );

add_filter( 'style_loader_src', 'filter_cache_busting_file_src' );