Simple way to return relative urls with wordpress built in wp_enqueue_* function. Good for caching!

functions.php

<?php

/**
 * cut the base url from the assets
 *
 * @param $src
 * @param $handle
 * @return mixed
 */
function make_urls_relative($src, $handle)
{
    if (strpos(get_bloginfo('url'), 'https') === 0) {
        $search = array(
            get_bloginfo('url'),
            str_replace('https', 'http', get_bloginfo('url'))
        );
    } else {
        $search = get_bloginfo('url');
    }

    $relative_url = str_replace(
        $search,
        '',
        $src
    );

    return $relative_url;
}

add_action('script_loader_src', 'make_urls_relative');
add_action('style_loader_src', 'make_urls_relative');