show alert after changing

index.html

@@ -72,7 +72,12 @@
             fetch(URL, { method: "POST" })
                 .then(res => res.json())
                 .then(data => {
-                    console.log(data)
+                    console.log("server response:" + data)
+                    if (data.success) {
+                        alert("Track changed successfully!");
+                    } else {
+                        alert("Failed to change track: " + data.message);
+                    }
                 });
         }
 
@@ -122,6 +127,11 @@
                 .then(res => res.json())
                 .then(data => {
                     console.log("Server response:", data);
+                    if (data.success) {
+                        alert("Cars changed successfully!");
+                    } else {
+                        alert("Failed to change cars: " + data.message);
+                    }
                 });
         }