[wordpress] How to add Class in <li> using wp_nav_menu() in Wordpress?

I am using wp_nav_menu($args) and I want to add my_own_class CSS classname to the <li> element for getting the following result:

<li class='my_own_class'><a href=''>Link</a>

How to do that?

Adding Class to <li> tag without editing functions.php file:

1. Go to Appearance -> Menu -> Screen Options -> CSS Classes
2. You will get CSS Class option enabled in Menu Items Window

I added a class to easily implement menu arguments. So you can customize and include in your function like this:

include_once get_template_directory() . DIRECTORY_SEPARATOR . "your-directory" . DIRECTORY_SEPARATOR . "Menu.php";

<?php $menu = (new Menu('your-theme-location'))
            ->setMenuClass('your-menu')
            ->setMenuID('your-menu-id')
            ->setListClass('your-menu-class')
            ->setLinkClass('your-menu-link anchor') ?>
    
            // Print your menu
            <?php $menu->showMenu() ?>

<?php

class Menu
{
    private $args = [
        'theme_location' => '',
        'container' => '',
        'menu_id' => '',
        'menu_class' => '',
        'add_li_class' => '',
        'link_class' => ''
    ];

    public function __construct($themeLocation)
    {
        add_filter('nav_menu_css_class', [$this,'add_additional_class_on_li'], 1, 3);
        add_filter( 'nav_menu_link_attributes', [$this,'add_menu_link_class'], 1, 3 );

        $this->args['theme_location'] = $themeLocation;
    }

    public function wrapWithTag($tagName){
        $this->args['container'] = $tagName;
        return $this;
    }

    public function setMenuID($id)
    {
        $this->args['menu_id'] = $id;
        return $this;
    }

    public function setMenuClass($class)
    {
        $this->args['menu_class'] = $class;
        return $this;
    }

    public function setListClass($class)
    {
        $this->args['add_li_class'] = $class;
        return $this;
    }

    public function setLinkClass($class)
    {
        $this->args['link_class'] = $class;
        return $this;
    }

    public function showMenu()
    {
        return wp_nav_menu($this->args);
    }

    function add_additional_class_on_li($classes, $item, $args) {
        if(isset($args->add_li_class)) {
            $classes[] = $args->add_li_class;
        }
        return $classes;
    }

    function add_menu_link_class( $atts, $item, $args ) {
        if (property_exists($args, 'link_class')) {
            $atts['class'] = $args->link_class;
        }
        return $atts;
    }
}

How about just using str_replace function, if you just want to "Add Classes":

<?php
    echo str_replace( '<li class="', '<li class="myclass ',
        wp_nav_menu(
            array(
                'theme_location'    => 'main_menu',
                'container'         => false,
                'items_wrap'        => '<ul>%3$s</ul>',
                'depth'             => 1,
                'echo'              => false
            )
        )
    );
?>

Tough it is a quick fix for one-level menus or the menus that you want to add Classes to all of <li> elements and is not recommended for more complex menus

The correct one for me is the Zuan solution. Be aware to add isset to $args->add_li_class , however you got Notice: Undefined property: stdClass::$add_li_class if you haven't set the property in all yours wp_nav_menu() functions.

This is the function that worked for me:

function add_additional_class_on_li($classes, $item, $args) {
    if(isset($args->add_li_class)) {
      $classes[] = $args->add_li_class;
    }
    return $classes;
}
add_filter('nav_menu_css_class', 'add_additional_class_on_li', 1, 3);

use this filter nav_menu_css_class as shown below

function add_classes_on_li($classes, $item, $args) {
    $classes[] = 'nav-item';
    return $classes;
}
add_filter('nav_menu_css_class','add_classes_on_li',1,3);

UPDATE

To use this filter with specific menu

if ( 'main-menu' === $args->theme_location ) { //replace main-menu with your menu
    $classes[] = "nav-item"; 
}

Without walker menu it's not possible to directly add it. You can, however, add it by javascript.

$('#menu > li').addClass('class_name');

None of these responses really seem to answer the question. Here's something similar to what I'm utilizing on a site of mine by targeting a menu item by its title/name:

function add_class_to_menu_item($sorted_menu_objects, $args) {
    $theme_location = 'primary_menu';  // Name, ID, or Slug of the target menu location
    $target_menu_title = 'Link';  // Name/Title of the menu item you want to target
    $class_to_add = 'my_own_class';  // Class you want to add

    if ($args->theme_location == $theme_location) {
        foreach ($sorted_menu_objects as $key => $menu_object) {
            if ($menu_object->title == $target_menu_title) {
                $menu_object->classes[] = $class_to_add;
                break; // Optional.  Leave if you're only targeting one specific menu item
            }
        }
    }

    return $sorted_menu_objects;
}
add_filter('wp_nav_menu_objects', 'add_class_to_menu_item', 10, 2);

You can add a filter for the nav_menu_css_class action in your functions.php file.

Example:

function atg_menu_classes($classes, $item, $args) {
  if($args->theme_location == 'secondary') {
    $classes[] = 'list-inline-item';
  }
  return $classes;
}
add_filter('nav_menu_css_class', 'atg_menu_classes', 1, 3);

Docs: https://developer.wordpress.org/reference/hooks/nav_menu_css_class/

<?php
    echo preg_replace( '#<li[^>]+>#', '<li class="col-sm-4">',
            wp_nav_menu(
                    array(
                        'menu' => $nav_menu, 
                        'container'  => false,
                        'container_class'   => false,
                        'menu_class'        => false,
                        'items_wrap'        => '%3$s',
                                            'depth'             => 1,
                                            'echo'              => false
                            )
                    )
            );
?>

No need to create custom walker. Just use additional argument and set filter for nav_menu_css_class.

For example:

$args = array(
    'container'     => '',
    'theme_location'=> 'your-theme-loc',
    'depth'         => 1,
    'fallback_cb'   => false,
    'add_li_class'  => 'your-class-name1 your-class-name-2'
    );
wp_nav_menu($args);

Notice the new 'add_li_class' argument.

And set the filter on functions.php

function add_additional_class_on_li($classes, $item, $args) {
    if(isset($args->add_li_class)) {
        $classes[] = $args->add_li_class;
    }
    return $classes;
}
add_filter('nav_menu_css_class', 'add_additional_class_on_li', 1, 3);

HERE WordPress add custom class in wp_nav_menu links

OR you can add class <li class='my_own_class'><a href=''>Link</a></li> from admin panel:

1. Go to YOURSITEURL/wp-admin/nav-menus.php

2. open SCREEN OPTIONS

3. make checked CSS CLASSES, then you will see CSS Classes (optional) field in each menu link.