How to automatically version WordPress assets using their last modified time

Versioning your assets in WordPress is relatively straight-forward as the wp_register_script() and wp_register_style() functions both offer support for specifying a version as a function parameter.

It’s easy to use because you simply pass it a value but it’s also simple to forget which could result in site visitors loading up stale versions of CSS and JS from a cache.

Thankfully, PHP provides us with an easy method of ensuring the version parameter changes whenever the file changes.

<?php

add_action( 'wp_enqueue_scripts', function () {

	$uri = get_stylesheet_directory_uri();
	$dir = get_stylesheet_directory();

	$script_last_updated_at = filemtime( "$dir/scripts/my-script.js" );
	$style_last_updated_at = filemtime( "$dir/styles/my-style.css" );

	wp_register_script( 'my-script', "$uri/scripts/my-script.js", [], $script_last_updated_at, true );
	wp_register_style( 'my-style', "$uri/styles/my-style.css", [], $style_last_updated_at, true );

} );