NODE JS introduction: socket polling

app/include_ending.php

@@ -7,6 +7,30 @@
 
 </div>
 
+<!-- ── Real-time WebSocket connection ──────────────────────────────────────── -->
+<!-- Socket.io client is served by the Node.js server itself                   -->
+<script src="<?php echo NODE_PUBLIC_URL; ?>/socket.io/socket.io.js"></script>
+<script>
+(function () {
+    // company_id is set in include_topbar.php as a JS global
+    if (typeof company_id === 'undefined' || !company_id) return;
+
+    window._socket = io('<?php echo NODE_PUBLIC_URL; ?>', {
+        query:           { company_id: company_id },
+        reconnection:    true,
+        reconnectionDelay: 2000,
+    });
+
+    window._socket.on('connect', function () {
+        console.log('[socket] connected', window._socket.id);
+    });
+
+    window._socket.on('disconnect', function () {
+        console.log('[socket] disconnected');
+    });
+})();
+</script>
+
 <!-- Stock rows modal — used by: order/order.php, order/return.php, po/po.php, po/supplier_returns.php (via show_stock_rows() in custom.js) -->
 <div class="modal fade" id="stock_rows_modal" tabindex="-1">
   <div class="modal-dialog modal-lg modal-dialog-scrollable">