How to add different menu items on different menus?

Question

This may sound weird, but I need to add different menu items to two specific menu types. When I mean different menu items, I mean, the items I set to main (header) menu are only for that menu and the same thing for footer menu. So, the menu items from primary-menu shouldn't appear on secondary-menu and vice-versa, despite how similar they seem to be.

  add_filter('wp_nav_menu_items', 'register_primary_menu_items', 10, 2);
  if (!function_exists('register_primary_menu_items')) {
    function register_primary_menu_items($items, $args) {
      if ( $args->menu = 'primary-menu' ) {
        $items .= "\n" . "\t\t\t\t\t\t" . '<li><a href="#home">Home</a></li>' . "\n" .
                 "\t\t\t\t\t\t" . '<li><a href="#main">Who are We</a></li>' . "\n" .
                 "\t\t\t\t\t\t" . '<li><a href="#service">Services</a></li>' . "\n" .
                 "\t\t\t\t\t\t" . '<li><a href="#contact">Contacts</a></li>' . "\n";
          //return $items;
      }
    /*
    if ( $args->theme_location = 'secondary-menu' ) {
        $items = '<li><i class="fa fa-angle-right"></i><a href="#home">Home</a></li>' . "\n" .
                 '<li><i class="fa fa-angle-right"></i><a href="#main">Who are We</a></li>' . "\n" .
                 '<li><i class="fa fa-angle-right"></i><a href="#service">Services</a></li>' . "\n" .
                 '<li><i class="fa fa-angle-right"></i><a href="#contact">Contacts</a></li>';
        return $items;
      }*/
        
      return $items;
    }
}

add_filter('wp_nav_menu_items', 'register_secondary_menu_items', 10, 2);
if (!function_exists('register_secondary_menu_items')) {
    function register_secondary_menu_items($items, $args) {
        if ( $args->menu = 'secondary-menu' ) {
            $items = "\n" . "\t\t\t\t\t\t" . '<li><i class="fa fa-angle-right"></i><a href="#home">Home</a></li>' . "\n" .
                     "\t\t\t\t\t\t" . '<li><i class="fa fa-angle-right"></i><a href="#main">Who are We</a></li>' . "\n" .
                     "\t\t\t\t\t\t" . '<li><i class="fa fa-angle-right"></i><a href="#service">Services</a></li>' . "\n" .
                     "\t\t\t\t\t\t" . '<li><i class="fa fa-angle-right"></i><a href="#contact">Contacts</a></li>' . "\n";
            //return $items;
          }
        return $items;
    }
}

That is the code I'm currently using, but it doesn't do what I want. Instead it sets the same menu items from secondary-menu on both header and footer menu or the inverse.

Answer 1

So, what was messing up with the menu items setting was assignment operator on the decision structure (condition) instead of comparison (or equal) operator to add the items based on menu location. I don't know how I missed or made that shameful kind of mistake.

Anyway, below is the working code template for WordPress menu editor in general that meets my needs. I had to replace menu argument with theme_location, menu wasn't working for me (Don't know why yet, and I doubt I have time to try to figure it out anyway).

add_filter('wp_nav_menu_items', 'register_header_footer_menu_items', 10, 2);
  if (!function_exists('register_header_footer_menu_items')) {
    function register_header_footer_menu_items($items, $args) {
      if ( $args->theme_location == 'primary-menu' ) {
        $items .= "\n" . "\t\t\t\t\t\t" . '<li><a href="#home">Home</a></li>' . "\n" .
                 "\t\t\t\t\t\t" . '<li><a href="#main">Who are We</a></li>' . "\n" .
                 "\t\t\t\t\t\t" . '<li><a href="#service">Services</a></li>' . "\n" .
                 "\t\t\t\t\t\t" . '<li><a href="#contact">Contacts</a></li>' . "\n";
          return $items;
      }
        
        if ( $args->theme_location == 'secondary-menu' ) {
            $items .= "\n" . "\t\t\t\t\t\t" . '<li><i class="fa fa-angle-right"></i><a href="#home">Home</a></li>' . "\n" .
                     "\t\t\t\t\t\t" . '<li><i class="fa fa-angle-right"></i><a href="#main">Who are We</a></li>' . "\n" .
                     "\t\t\t\t\t\t" . '<li><i class="fa fa-angle-right"></i><a href="#service">Services</a></li>' . "\n" .
                     "\t\t\t\t\t\t" . '<li><i class="fa fa-angle-right"></i><a href="#contact">Contacts</a></li>' . "\n";
            return $items;
          }
    }
}