different body classes for each category

Question

How can I add special classes ( like " japan japan_index" ) for body class in category-japan.php and for category.php something like this " archive archive_index " and also I'm using this code to put categories name on single.php and index.php body class

    // Adding categories name to body class
add_filter('body_class','add_category_to_single');
function add_category_to_single($classes) {
  if (is_single() ) {
    global $post;
    foreach((get_the_category($post->ID)) as $category) {
      // add category slug to the $classes array
      $classes[] = $category->category_nicename;
    }
  }
    else{
        $classes[] = 'index';
    }
  // return the $classes array
  return $classes;
}

// Allowed classes
add_filter( 'body_class', 'remove_some', 10, 2 );
function remove_some( $wp_classes, $extra_classes ) {

    // List of the only WP generated classes allowed
    $whitelist = array( 'index', 'japanese', 'japan', 'interviews', 'travel', 'reviews', 'series', 'archive' );

    // Filter the body classes
    $wp_classes = array_intersect( $wp_classes, $whitelist );

    // Add the extra classes back untouched
    return array_merge( $wp_classes, (array) $extra_classes );
}

Answer 1

If i understood what you are lookin for, this should work, it uses get_queried_object() function:

// Adding categories name to body class on archives
add_filter('body_class','add_category_to_body_class');
function add_category_to_body_class( $classes ) {
    // check if in category
    if ( is_category() ) {
        // get the queried object, in this case, a category object, and assigns to a variable
        // see https://codex.wordpress.org/Function_Reference/get_queried_object
        $category_object = get_queried_object();
        // get the slug
        $classes[] = $category_object->slug;
        $classes[] = $category_object->slug . '_index';
    }
  // return the $classes array
  return $classes;
}

but you can mix it to your single function:

// Adding categories name to body class on archives
add_filter('body_class','add_category_to_body_class');
function add_category_to_body_class( $classes ) {
    if ( is_single() ) {
        global $post;
        // assigns post it to variable to avoid reading an array for every loop iteration
        // maybe a micro optmization? Guilty as charged!
        $post_id = $post->ID;
        foreach( ( get_the_category( $post_id ) ) as $category ) {
            // add category slug to the $classes array
            $classes[] = $category->category_nicename;
            $classes[] = $category->category_nicename . '_index';
        }
    }
    // check if in category
    else if ( is_category() ) {
        // get the queried object, in this case, a category object, and assigns to a variable
        // see https://codex.wordpress.org/Function_Reference/get_queried_object
        $category_object = get_queried_object();
        // get the slug
        $classes[] = $category_object->slug;
        $classes[] = $category_object->slug . '_index';
    }
    else {
        $classes[] = 'index';
    }
    // return the $classes array
    return $classes;
}

I hope it helps.