0

I was trying to add css class to nav items.

The documented function call in WordPress docs was

apply_filters( 'nav_menu_css_class', string[] $classes, WP_Post $item, stdClass $args, int $depth )

But I tried adding the following to functions.php in my child theme doesn't work.

apply_filters('nav_menu_css_class', ['nav-item']);

But the adding the following to functions.php works as expected.

add_filter('nav_menu_css_class', fn () => ['nav-item']);

Why do add_filter works but not apply_filters?

1 Answer 1

0

Because that's not what apply_filters() does. You'll even see the usage guide and examples at your link all use add_filter(). Also see the official docs on Filters.

Using apply_filters() makes a value filterable. add_filter() is used to filter a filterable value by passing a function that does the filtering.

WordPress uses apply_filters('nav_menu_css_class', ..., which allows you to use add_filter() to modify its value. So if you want to modify the nav menu CSS classes, you need to add a filter, with add_filter().

The reason apply_filters() is shown in the docs you linked is because it's showing how that filter was originally defined. Not how to use it.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.