Adding custom fields above WOOCOMMERCE add to cart button

gistfile1.php

<?php

// To add custom data above add to cart button in woocommerce

// step 1

add_action('wp_ajax_wdm_add_user_custom_data_options', 'wdm_add_user_custom_data_options_callback');
add_action('wp_ajax_nopriv_wdm_add_user_custom_data_options', 'wdm_add_user_custom_data_options_callback');

function wdm_add_user_custom_data_options_callback()
{
    //Custom data - Sent Via AJAX post method
    $product_id = $_POST['id']; //This is product ID
    $custom_data_1 = $_POST['custom_data_1']; //This is User custom value sent via AJAX
    $custom_data_2 = $_POST['custom_data_2'];
    $custom_data_3 = $_POST['custom_data_3'];
    $custom_data_4 = $_POST['custom_data_4'];
    $custom_data_5 = $_POST['custom_data_5'];


    session_start();
    $_SESSION['custom_data_1'] = $custom_data_1;
    $_SESSION['custom_data_2'] = $custom_data_2;
    $_SESSION['custom_data_3'] = $custom_data_3;
    $_SESSION['custom_data_4'] = $custom_data_4;
    $_SESSION['custom_data_5'] = $custom_data_5;
    die();
}

// step 2

add_filter('woocommerce_add_cart_item_data','wdm_add_item_data',1,2);

if(!function_exists('wdm_add_item_data'))
{
    function wdm_add_item_data($cart_item_data,$product_id)
    {
        /*Here, We are adding item in WooCommerce session with, wdm_user_custom_data_value name*/
        global $woocommerce;
        session_start();

        $new_value = array();


        if (isset($_SESSION['custom_data_1'])) {
            $option1 = $_SESSION['custom_data_1'];
            $new_value['custom_data_1'] =  $option1;
        }
        if (isset($_SESSION['custom_data_2'])) {
            $option2 = $_SESSION['custom_data_2'];
            $new_value['custom_data_2'] =  $option2;
        }
        if (isset($_SESSION['custom_data_3'])) {
            $option3 = $_SESSION['custom_data_3'];
            $new_value['custom_data_3'] =  $option3;
        }
        if (isset($_SESSION['custom_data_4'])) {
            $option4 = $_SESSION['custom_data_4'];
            $new_value['custom_data_4'] =  $option4;
        }
        if (isset($_SESSION['custom_data_5'])) {
            $option5 = $_SESSION['custom_data_5'];
            $new_value['custom_data_5'] =  $option5;
        }

        if( empty($option1) && empty($option2) && empty($option3) && empty($option4) && empty($option5)  )
            return $cart_item_data;
        else
        {
            if(empty($cart_item_data))
                return $new_value;
            else
                return array_merge($cart_item_data,$new_value);
        }


//        vardump($new_value);
//        die();


        unset($_SESSION['custom_data_1']);
        unset($_SESSION['custom_data_2']);
        unset($_SESSION['custom_data_3']);
        unset($_SESSION['custom_data_4']);
        unset($_SESSION['custom_data_5']);

        //Unset our custom session variable, as it is no longer needed.
    }
}

// step 3

add_filter('woocommerce_get_cart_item_from_session', 'wdm_get_cart_items_from_session', 1, 3 );
if(!function_exists('wdm_get_cart_items_from_session'))
{
    function wdm_get_cart_items_from_session($item,$values,$key)
    {

        if (array_key_exists( 'custom_data_1', $values ) )
        {
            $item['custom_data_1'] = $values['custom_data_1'];
        }

        if (array_key_exists( 'custom_data_2', $values ) )
        {
            $item['custom_data_2'] = $values['custom_data_2'];
        }

        if (array_key_exists( 'custom_data_3', $values ) )
        {
            $item['custom_data_3'] = $values['custom_data_3'];
        }

        if (array_key_exists( 'custom_data_4', $values ) )
        {
            $item['custom_data_4'] = $values['custom_data_4'];
        }

        if (array_key_exists( 'custom_data_5', $values ) )
        {
            $item['custom_data_5'] = $values['custom_data_5'];
        }

        return $item;
    }
}


// step 4

add_filter('woocommerce_checkout_cart_item_quantity','wdm_add_user_custom_option_from_session_into_cart',1,3);
add_filter('woocommerce_cart_item_price','wdm_add_user_custom_option_from_session_into_cart',1,3);

if(!function_exists('wdm_add_user_custom_option_from_session_into_cart'))
{
    function wdm_add_user_custom_option_from_session_into_cart($product_name, $values, $cart_item_key )
    {
        /*code to add custom data on Cart & checkout Page*/
        if(count($values['custom_data_1']) > 0)
        {
            $return_string = $product_name . "</a><dl class='variation'>";
            $return_string .= "<table class='wdm_options_table' id='" . $values['product_id'] . "'>";
            $return_string .= "<tr><td> custom_data_1 : " . $values['custom_data_1'] . "</td></tr>";
            $return_string .= "<tr><td> custom_data_2 : " . $values['custom_data_2'] . "</td></tr>";
            $return_string .= "<tr><td> custom_data_3 : " . $values['custom_data_3'] . "</td></tr>";
            $return_string .= "<tr><td> custom_data_4 : " . $values['custom_data_4'] . "</td></tr>";
            $return_string .= "<tr><td> custom_data_5 : " . $values['custom_data_5'] . "</td></tr>";
            $return_string .= "</table></dl>";

            return $return_string;
        }
        else
        {
            return $product_name;
        }
    }
}


// step 5

add_action('woocommerce_add_order_item_meta','wdm_add_values_to_order_item_meta',1,2);
if(!function_exists('wdm_add_values_to_order_item_meta'))
{
    function wdm_add_values_to_order_item_meta($item_id, $values)
    {
        global $woocommerce,$wpdb;


        $user_custom_values = $values['wdm_user_custom_data_value'];

        if(!empty($user_custom_values))
        {
            wc_add_order_item_meta($item_id,'wdm_user_custom_data',$user_custom_values);
        }
        
        $custom_data_1 = $values['custom_data_1'];

        if(!empty($custom_data_1))
        {
            wc_add_order_item_meta($item_id,'custom_data_1',$custom_data_1);
        }

        $custom_data_2 = $values['custom_data_2'];

        if(!empty($custom_data_2))
        {
            wc_add_order_item_meta($item_id,'custom_data_2',$custom_data_2);
        }

        $custom_data_3 = $values['custom_data_3'];

        if(!empty($custom_data_3))
        {
            wc_add_order_item_meta($item_id,'custom_data_3',$custom_data_3);
        }

        $custom_data_4 = $values['custom_data_4'];

        if(!empty($custom_data_4))
        {
            wc_add_order_item_meta($item_id,'custom_data_4',$custom_data_4);
        }

        $custom_data_5 = $values['custom_data_5'];

        if(!empty($custom_data_5))
        {
            wc_add_order_item_meta($item_id,'custom_data_5',$custom_data_5);
        }
    }
}


// step 6

add_action('woocommerce_before_cart_item_quantity_zero','wdm_remove_user_custom_data_options_from_cart',1,1);
if(!function_exists('wdm_remove_user_custom_data_options_from_cart'))
{
    function wdm_remove_user_custom_data_options_from_cart($cart_item_key)
    {
        global $woocommerce;
        // Get cart
        $cart = $woocommerce->cart->get_cart();
        // For each item in cart, if item is upsell of deleted product, delete it
        foreach( $cart as $key => $values)
        {
            if ( $values['wdm_user_custom_data_value'] == $cart_item_key )
                unset( $woocommerce->cart->cart_contents[ $key ] );
        }
    }
}

?>

// I m using following script in my template which is working perfect

<script type="text/javascript">

    jQuery(document).ready(function(){
        //code to add validation on "Add to Cart" button
        jQuery('.single_add_to_cart_button').click(function(){
            //code to add validation, if any
            //If all values are proper, then send AJAX request

            alert('sending ajax request');

            var custom_data_1 = 'custom_data_1';
            var custom_data_2 = 'custom_data_2';
            var custom_data_3 = 'custom_data_3';
            var custom_data_4 = 'custom_data_4';
            var custom_data_5 = 'custom_data_5';


            var ajaxurl = '<?php echo admin_url('admin-ajax.php'); ?>';

            jQuery.ajax({
                url: ajaxurl, //AJAX file path - admin_url('admin-ajax.php')
                type: "POST",
                data: {
                    //action name
                    action:'wdm_add_user_custom_data_options',
                    custom_data_1 : custom_data_1,
                    custom_data_2 : custom_data_2,
                    custom_data_3 : custom_data_3,
                    custom_data_4 : custom_data_4,
                    custom_data_5 : custom_data_5

                },
                async : false,
                success: function(data){
                    //Code, that need to be executed when data arrives after
                    // successful AJAX request execution

                    alert('ajax response recieved');


                }
            });
        })
    });


</script>

Hello everyone, brad new to WC, does this code work for woocommerce 3+?

Where do I need to write java script code

I was able to follow the code up to last part with the javascript code and I understand that is what what will make the function in step 1 run. My questioin is: "After running the function in step 1, how do the other functions get called?

How to add different meta values .
Like On one button click i want to add
a
b
c
Then on other button click on want to add
e
f
g
Then how i can sort that on cart page with product ID?

Sorry, not work:

if(count($values['custom_data_1']) > 0) Undefine index custom_data_1

help please

I'm giving a solution for woocomerce 3+, for lower versions it's also on this page. https://wisdmlabs.com/blog/add-custom-data-woocommerce-order-2/