I released a plugin that creates a shortcode and requires a JavaScript file and a CSS file to load on any page that contains that shortcode. I could just make the script/style load on all pages, but that's not the best practice. I only want to load the files on pages that call the shortcode. I've found two methods of doing this, but both have problems.
Method 1 sets a flag to true inside the shortcode handler function, and then checks that value inside a wp_footer callback. If it's true, it uses wp_print_scripts() to load the JavaScript. The problem with this is that it only works for JavaScript and not CSS, because CSS should be declared inside <head>, which you can only do during an early hook like init or wp_head.
Method 2 fires early and "peeks ahead" to see if the shortcode exists in the current page content. I like this method much better than the first, but the problem with it it won't detect if the template calls do_shortcode().
So, I'm leaning towards using the second method and then trying to detect if a template is assigned, and if so, parse it for the shortcode. Before I do that, though, I wanted to check if anyone knows of a better method.
NOTE: Any acceptable solution needs to follow best practices, which means that all CSS has to go inside <head>, and wp_enqueue_script()/wp_enqueue_style() are used to load files. I already know there are methods that get around this by implementing bad practices, but I'm not interested in those. Please don't answer/comment if your solution doesn't meet that critera.
Update: I've integrated the solution into my plugin. If anyone is curious to see it fleshed out in a live environment you can download it or browse it.
Update 2: As of WordPress 3.3, it's now possible to call wp_enqueue_script() directly inside a shortcode callback, and the JavaScript file will be called within the document's footer. That's technically possible for CSS files as well, but should be considered a bad practice because outputting CSS outside the <head> tag violates W3C specs, can case FOUC, and may force the browser to re-render the page.