fill in datat on checkout page

prijs-per-postcode.php

@@ -1,5 +1,6 @@
 <?php
 
+session_start();
 require_once "session_dialog.php";
 /*
  * Plugin Name: Prijs per Postcode
@@ -26,6 +27,34 @@ class PrijsPerPostcode
     {
         $uri = $_SERVER["REQUEST_URI"];
         if_needed_place_postcode_form($uri);
+
+        add_action("wp_footer", "set_checkout_fields_with_javascript");
+        function set_checkout_fields_with_javascript()
+        {
+            // Only run on the checkout page
+            if (!is_checkout() || is_wc_endpoint_url()) {
+                return;
+            }
+
+            // Define the values you want to set
+            $woonplaats = $SESSION["woonplaats"];
+            $postcode = $_SESSION["postcode"];
+            $address_1 =
+                $_SESSION["straatnaam"] . " " . $_SESSION["huisnummer"];
+            // Output the JavaScript
+            ?>
+            <script type="text/javascript">
+            jQuery(document).ready(function($){
+                // Set the values for the checkout fields
+                $('#billing_city').val('<?php echo esc_js($woonplaats); ?>');
+                $('#billing_postcode').val('<?php echo esc_js($postcode); ?>');
+                $('#billing_address_1').val('<?php echo esc_js(
+                    $address_1,
+                ); ?>');
+            });
+            </script>
+            <?php
+        }
     }
 }