tweaking the <title>

Question

so I wanted to change the <title> head element and found this post: Change the_title() of a page dynamically

I followed and my function now looks like this:

# set title per page
function vendor_module_filter_the_title($title)
{
    # exclude menus
    if (!in_the_loop()) {return $title;}

    # collection page
    if (is_page_template('page-collection.php')) {
        if (strpos($_SERVER['REQUEST_URI'], 'category1') !== false) {
            $title = 'title 1';
        } else if (strpos($_SERVER['REQUEST_URI'], 'category2') !== false) {
            $title = 'title 2';
        }
    }

    return $title;
}

add_filter('the_title', 'vendor_module_filter_the_title', 10, 2);

however after CTRL + F5 it doesn't seem to work, I've tested with other meta tags using add_action('wp_head', ...) but it doesn't seem to work for title using add_filter - how do I go about debugging? How do I find out why this function doesn't work?

where am I going wrong? :/

Answer 1

the answer (taken from: https://stackoverflow.com/questions/36087390/add-filterwp-title-doesnt-replace-my-title-tag-wordpress-plugin) was to do this:

add_filter( 'pre_get_document_title', 'vendor_module_filter_the_title', 999, 1 );

this is due to the YOAST SEO plugin and the above is the found workaround.