Create your own HTML code for the wp_nav_menu()

Example of Walker_Nav_Menu class extension, to create your own custom HTML code which is outputs by function wp_nav_menu(). Our HTML code will be written specifically for our theme.

Below is the code of its own arbitrary class that builds the menu. It adds menu depth and even/odd CSS classes to menu elements (both ul and li):

To avoid reinventing the wheel, we copy the code of the Walker_Nav_Menu{} class and just modify it as we need.

/**
 * Custom walker class for nav menus.
 */
class My_Walker_Nav_Menu extends Walker_Nav_Menu {

	/**
	 * Adds classes to ul sub-menus.
	 *
	 * @return void
	 */
	function start_lvl( &$output, $depth = 0, $args = null ) {
		// depth dependent classes
		$indent = ( $depth > 0  ? str_repeat( "\t", $depth ) : '' ); // code indent
		$display_depth = ( $depth + 1); // because it counts the first submenu as 0
		$classes = [
			'sub-menu',
			( $display_depth % 2 ? 'menu-odd' : 'menu-even' ),
			( $display_depth >= 2 ? 'sub-sub-menu' : '' ),
			'menu-depth-' . $display_depth,
		];
		$class_names = implode( ' ', $classes );

		$output .= "\n" . $indent . '<ul class="' . $class_names . '">' . "\n";
	}

	//

	/**
	 * Adds main classes to li's and links.
	 *
	 * @return void
	 */
	function start_el( &$output, $data_object, $depth, $args, $current_object_id = 0 ) {
		$item = $data_object; // use more descriptive name for use within this method.

		$indent = ( $depth > 0 ? str_repeat( "\t", $depth ) : '' ); // code indent

		// depth dependent classes
		$depth_classes = [
			( $depth == 0 ? 'main-menu-item' : 'sub-menu-item' ),
			( $depth >= 2 ? 'sub-sub-menu-item' : '' ),
			( $depth % 2 ? 'menu-item-odd' : 'menu-item-even' ),
			'menu-item-depth-' . $depth,
		];
		$depth_class_names = esc_attr( implode( ' ', $depth_classes ) );

		// passed classes
		$classes = empty( $item->classes ) ? [] : (array) $item->classes;
		$class_names = esc_attr( implode( ' ', apply_filters( 'nav_menu_css_class', array_filter( $classes ), $item ) ) );

		// build html
		$output .= $indent . '<li id="nav-menu-item-'. $item->ID . '" class="' . $depth_class_names . ' ' . $class_names . '">';

		// link attributes
		$attributes  = ! empty( $item->attr_title ) ? ' title="'  . esc_attr( $item->attr_title ) .'"' : '';
		$attributes .= ! empty( $item->target )     ? ' target="' . esc_attr( $item->target     ) .'"' : '';
		$attributes .= ! empty( $item->xfn )        ? ' rel="'    . esc_attr( $item->xfn        ) .'"' : '';
		$attributes .= ! empty( $item->url )        ? ' href="'   . esc_attr( $item->url        ) .'"' : '';
		$attributes .= ' class="menu-link ' . ( $depth > 0 ? 'sub-menu-link' : 'main-menu-link' ) . '"';

		$item_output = strtr( '{BEFORE}<a{ATTRIBUTES}>{LINK_BEFORE}{TITLE}{LINK_AFTER}</a>{AFTER}', [
			'{BEFORE}'      => $args->before,
			'{ATTRIBUTES}'  => $attributes,
			'{LINK_BEFORE}' => $args->link_before,
			'{TITLE}'       => apply_filters( 'the_title', $item->title, $item->ID ),
			'{LINK_AFTER}'  => $args->link_after,
			'{AFTER}'       => $args->after,
		] );

		$output .= apply_filters( 'walker_nav_menu_start_el', $item_output, $item, $depth, $args );
	}

}

Now that the class is ready, use it in wp_nav_menu() function. To do this, specify an instance of our class in the walker parameter.

function my_nav_menu( $args ) {

	$args = array_merge( [
		'container'       => 'div',
		'container_id'    => 'top-navigation-primary',
		'container_class' => 'top-navigation',
		'menu_class'      => 'menu main-menu menu-depth-0 menu-even',
		'echo'            => false,
		'items_wrap'      => '<ul id="%1$s" class="%2$s">%3$s</ul>',
		'depth'           => 10,
		'walker'          => new My_Walker_Nav_Menu()
	], $args );

	echo wp_nav_menu( $args );
}

Now use our function wherever you want to display the menu:

my_nav_menu( [
	'theme_location'  => 'navigation_menu_primary'
] );